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.
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.
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.
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.
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.
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.
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.
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.
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)
The price is a flat rate of $99 instead of paying $19.99 a month for a year or $29.99 a month for Photoshop or Illustrator. Plus there is a free trial to check Sketch out.
myBalsamiq has been built with teams in mind and has a variety of featured to support collaborating on the mockups:
Notifications - Real-time notifications to enable you to keep track of team member actions
Revision Control - All mockups have a revision history to enable reverting to previous versions and keeping track of design decisions.
Skype Integration - Easy to use Skype integration to host design reviews.
Access Control - Access controls allow sharing projects with team members as well as allowing external reviewers to leave comments on the designs.
Balsamiq has a very easy to use drag and drop interface that lets you quickly build and adjust your mockups. The UI is centered around low-fidelity wireframes that help focus the reviews on the core layout and functionality instead of getting hung-up on visual design.
Doing anything that is not directly supported by Balsamiq's conservative component library is next to impossible. User is forced to think within the corset of yesterday's standards.
Adobe Experience Design is simplistic and easy to use. After all, mockups should be quick and easy to made as opposed to using tools like Sketch to make them which are complicated and suitable for design professionals.
As part of Adobe package, it's okay for Wireframing, but there are so many things to improve. Ability to scroll (envision does a great job on it), Create Architectures of a website/app, style on click. And the biggest one, Not to have to duplicate a screen just to add a modal on a view.
There is a wealth of online training including videos for getting the basics down, a great community to mine, and support team to help assist with more technical details.