When comparing Inkscape vs Sketch, the Slant community recommends Inkscape for most people. In the question“What are the best vector graphics editors?” Inkscape is ranked 1st while Sketch is ranked 9th. The most important reason people chose Inkscape is:
Inkscape is GPL-licensed and maintains public repositories.
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro Free and open source
Inkscape is GPL-licensed and maintains public repositories.

Pro Opens lots of file types
Inkscape supports many common formats for import (including SVG, Photoshop and Illustrator) and its plugin architecture allows more to be added.
Pro Export to different file types
Files can be exported and saved as a "normal" svg, png, jpg, bmp etc. file.

Pro Cross-platform
Pre-built binaries are available for Windows, Mac and Linux. Inkscape can be built from source on additional platforms.
Pro Integrates well into a X11-System
Its uses the X11 icon theme and desktop theme(GTK).
Pro It can do anything
A very powerful software that can do pretty match anything!
Pro Measurement Tool
This tool is extremely handy and can not be found in any other vector graphics programs out there.
Pro Live Path Effects
Extremely powerful menu that offers more than 30 powerful Live Path Effects to apply to paths vastly enhancing the application functionality.
Pro Guides, Grids, and Canvas Rotation
Extremely handy features when building complex graphics using Inkscape.
Pro Dark Theme Support
The new 1.0 beta 2 version finally got support for dark theme which normally is only available for commercial software like Affinity Serif, Adobe Illustrator.
Pro The new version 1.1 is looks and feels fantastic
Inskape got UI update: new dockable dialogs.
Pro Interface is available in 29 languages
Basque, British English, Brazilian, Portuguese, Catalan, Croatian, Czech, Dutch, Finnish, French, German, Greek, Hindi, Hungarian, Icelandic, Indonesian, Italian, Korean, Latvian, Norwegian (Bokmål), Polish, Romanian, Russian, Slovak, Spanish, Swedish, Turkish, Ukrainian, Urdu, Swedish.
Pro It's really easy and fun
Vector graphics can be created and edited with Inkscape.
Pro Designed specifically for web and mobile UI design & workflows
Sketch is essentially a version of Photoshop built from the ground up to suit the workflow of web designers.
Pro Active community with a lot of resources
Sketch is hugely popular among designers so there are a lot of well maintained community resources for everything from iPhone frames to iOS/Android UI elements & icons.
Pro Clean UI
Reactive panels keep the UI for Sketch clean from the sort of clutter the panel system in Photoshop suffers from. The panels in Sketch change based on the object in question, saving you from having to have a multiple separate panels.
Pro Symbols and shared styles
Sketch lets you re-use the same design in multiple places, with changes synced throughout the various places it is used. You can also create text styles to sync typography changes.
Pro "Artboards" are great for working on multiple views simultaneously
Artboards let you easily work on multiple views side by side. Great for having a separate artboard on each page for the various responsive sizes.
Pro Vector based yet pixel aware
You can rescale assets without quality loss, easily export x2 assets for retina designs and design high quality icons & artwork. Being pixel aware lets you set a grid and snap objects to it as well as round to the nearest pixel edge to clean up your layers.
Pro Makes it easy to export assets
Sketch has a built in exporter that supports PDF, JPG and PNG.
Pro Built-in grid system
You can set the square grid to whatever dimensions you like as well as set thicker lines every x blocks. You can also configure the color of the lines to make them as obvious or subtle as you wish and toggle the grid with a keyboard shortcut (crtl+g).
Pro "Mirror" makes it really easy to test designs on multiple devices
Mirror lets you connect your iPhone to sketch and see how your current artboard looks on mobile. It's really useful as you can live check changes which lets you rapidly iterate mobile design.
Pro Easily align layers with smart guides
Holding down alt will show the smart guides that show the distances between any layer you hover over to nearby layers or the edges of the artboard. Very useful for checking your spacing or aligning layers.
Cons

Con Very slow startup on some systems
Depending on factors like how many fonts you have installed, Inkscape can take upwards of 30 seconds to launch.
Con Uses its own SVG-format by default
Inkscape might use SVG as its default format, however this SVG's contains some additional SodiPodi/Inkscape additions that can be troublesome if you want to import the SVG into some other application.
Con 1.0 is sluggish
Inkscape 1.0 uses GTK 3 which is sluggish and slow for low spec systems( eg. ARM, Celeron, Pentium, Core-i3, Ryzen 3 or Athlon ) compared to previous versions.
Con Buggy
Application is often buggy so it happens from time to time that the popup / right-click menu won't close and stays open. It crashes also sometimes randomly. This makes it almost unusable for productive / business use.
Con Crashes very often
Inkscape encountered an internal error and will close now - is one of its standard messages.
Con Since 0.91 the gradient editor is gone
It is now only possible to edit a gradient on screen. but you can't set a stop to a specific percentage anymore.
Con Limited work with ICC CMYK color scheme
Support for ICC color profiles only in SVG files.
Con Y-axis inverted
0,0 coordinates begin in lower left corner, not upper left corner as SVG standards define in Inkscape 0.92.x.
It seems this is now fixed in the 1.0 beta 2 version of the program.
Con Uses GTK
It looks an feels like an alien. It also uses now touch-based widgets instead of professional widgets.
Con A toy for facebook-ist enthusiasts, not for professionals
It's a Linux niche mumbo-jumbo, same as GIMP for raster edit .
Con Based on the GTK widget toolkit
Software is based on GTK, so it might not integrate well in non-GTK environments. It also requires many dependencies on those non-GTK desktops. It also adds dependencies to GTK-environments since it is written in C++ which requires the gtkmm wrapper/interface.
Con Mac version does not look as polished as its versions for Windows/Linux version for the 0.92.x version
It seems that Inkscape 1.0 beta 2 for Mac got some needed attention and it looks a lot better with dark theme support. native DMG installer and they got rid of X11 which is great.
Con Incompatible with previous versions
Sometimes backward compatibility breaks. For example, pre 0.92 SVGs are incompatible with later releases (due different default resolutions).
Con No support for large printing machine system
No support for large printing machine environment, except exporting the resulting artwork to PDF.
Con Under GNU GPL
It is released under GNU GPL which one of the restricted open source license.
Con No Windows support
Con No Linux version
Sketch is currently only available on Mac, which can make it hard to collaborate if you have teammates using Linux.
Con License based payment model
Sketch has recently decided to cease development of major version (2.0, 3.0, 4.0) with free updates in between, and has switched to a license based subscription model. A yearly license costs $99 and includes the latest version of the Sketch software, plus a year of free updates. After this license expires, you can renew for another year of updates - or continue to use the current software without updates.
Con Buggy releases and lack of quality assurance
The fast rate of change means new releases often break files and cause havoc. Duplicate symbols are really bad in the latest releases so you have to keep updating.
Con Very feeble raster tools
You have to go elsewhere if you want something more complex than basic vector masking of raster images.
Con Limited compatibility with Photoshop and Illustrator
Although it is possible to export certain Adobe file types in Sketch, compatibility is mostly hit and miss. For example, some elements seem a little offset in Adobe products.
