When comparing Double Commander vs FTP Synchronizer, the Slant community recommends Double Commander for most people. In the question“What are the best GUI file managers for UNIX-like systems?” Double Commander is ranked 4th while FTP Synchronizer is ranked 19th. The most important reason people chose Double Commander is:
You can use same tool in all desktop OS environments.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Multi-platform (Linux, Windows, MacOS X)
You can use same tool in all desktop OS environments.
Pro Source code is available (true free software)
If the developer loses interest there is at least the possibility that someone else will pick up the torch.
Pro Configurable
Lots of options allow you to configure DC the way it suits you best: Tools, Fonts, Colors, Hotkeys, Mouse, Fileviews, Plugins, Layout, Toolbars, Tabs, Icons etc.
Pro Directory Hotlist
Save shortcuts to folders. Organize them in a treeview with submenus. Define a name and sorting for each entry.
Pro Powerful tcmd-like search tool (alt+F7)
Pro tcmd-like multi-rename tool (CTRL+M)
Pro DC uses TCmd plugin API
so you can use documentation from Total Commander for writing plugins. WCX (packer), WDX (content), WFX (file system), WLX (lister).
Pro Closely follows TotalCommander UX
For instance, the 'Settings | Layout' pane is quasi-identical to TCs.
Pro Very sophisticated
Although it is lightweight and simple to use, it can do very sophisticated tasks, like copying files from directories which have a certain extension or file size or have a certain text pattern in them. Also, it's very customizable and stable.
Pro It's that good, you can replace tcmd on windows too
Pro Source code written in (Object) PASCAL
It's all a matter of perspective. I'm not for an argument about IDE's, frameworks etc, but to me that's a big plus. I think it should be a tie, it's either a pro or a con or should that be neither a pro nor a con. It just depends on context.
Pro Can sync multiple files across multiple websites in parallel
With FTP Synchronizer you can synchronize multiple files and multiple sites simultaneously.
Pro Can schedule syncs
You can schedule when you want to synchronize a particular document for a particular website.
Pro Very secure
Supports syncing over FTPS and SFTP.
Pro Does not waste time by copying every file over
When syncing a folder, FTP Synchronizer intelligently finds out which files have been changed and copies only them.
Cons

Con Apparently only one developer
Con Freeze after mouse double-click on directory list item
Con Much slower on Linux and Mac than on Windows
Con Source code written in Pascal language
But this does not affect users negatively. It's just programmers problem.
Con Not developed anymore for Mac
Con Can't edit files on remote FTP servers
Con Overpriced
Even using single license mode no longer functions correctly. No longer sending emails as it says it does.
