When comparing Transmit vs ForkLift 3, the Slant community recommends Transmit for most people. In the question“What are the best FTP clients for OS X?” Transmit is ranked 1st while ForkLift 3 is ranked 7th. The most important reason people chose Transmit is:
The app is Beautiful and easy to use, as well looks amazing alongside other osx apps.
Specs
Ranked in these QuestionsQuestion Ranking
Pros

Pro Beautiful and easy to use
The app is Beautiful and easy to use, as well looks amazing alongside other osx apps.
Pro Supports Amazon S3 & WebDAV
In addition to FTP, allows exchanging data with SFTP or WebDAV servers or your Amazon S3 storage.
Pro Can enable a server connection as a normal disk in your Finder
So you can access your storage without the Transmit client.
Pro FTP Sync
Scans local and remote for difference and only transfer modified files. It's not rsync, but it's the next best thing
Pro Fastest file upload and download
Pro Long term reliability
We're using Transmit for at least a decade with all our client's sites. It just works and it blends into our MacOS workflow seamlessly -- what more can you ask for? If you don't want to pay for a license, you'll pay with your time.
Pro Best UX/UI'd file manager on the market
It's just a perfectly crafted app, try and enjoy
Pro Rewritten in Swift
Forklift 3 is a significant update from FL2, having been rewritten entirely in Swift.
Pro Optional dark UI
In addition to the default Mac gray UI, Forklift 3 offers an alternate "Dark Mode" featuring light text elements against dark backgrounds.
Pro Connect to and mount lots of storage options
FTP, WebDAV, Amazon S3, Backblaze B2, Google Drive, Rackspace CloudFiles, SMB, AFP, NFS, VNC, etc.
Pro Easily toggle hidden files
Pro Built-in application remover
Cons
Con Need to pay for license
Con Like Apple, it does not standardize file size. Mixes up KBs, MBs GBs in the same column which makes it very difficult to review file sizes
Con Like Apple, shows the date of Today's file as "Today" instead of the actual date
Con Does not sync the "selected" folders (i.e. highlighted ones), but the "current" folders (i.e. the top of the visible tree.)
Con Does not show the fixed tree section in the left pane of a dual horizontal panes
