The 6 is good. More power on the channels so you can safely directly attach pumps with no heat or overload worries. PWM on all channels too.
The heatsink makes it look a lot nicer, cools it and gives it a bit of protection.
The remote I've never used more than once but in theory you can set up the unit (type in names etc) but you'd do that more easily using Aquasuite and a keyboard. It could be of interest for a media system I suppose. It can emulate a mouse and keyboard.
Touch buttons are dependant upon whether you like them. The same functionality can be had by mechanical buttons apart from the shortcuts along the bottom of the screen...that you never use. To be blunt, apart from scrolling through to see what raised an alarm if problems happen, you'll likely never use the buttons once you've set it up with Aquasuite. Largely it comes down to looks to be honest. If you're thinking of stripping the screen off, get whichever is cheapest as you'd take off bezel, touchscreen, screen and IR receiver (for remote) when you do.
Worth mentioning that the XT will come with a license for Aquasuite 2017-2019 but a Pro will only get 2017-2018. Not a big consideration but worth a note.