You really need to get your hands on them, literally.
I have worked professionally with a drill in hand for the last fifteen years and I can't even decide which Festool drill I like the best. Maybe because none of them are perfect, so far.
The T18 is arguably the best allrounder for weight, flexibility and performance. It has a "normal" grip which is nice and takes compact high performance batteries as well as larger higher Ah batteries if needed.
The CXS is my go to drill for small work and assembly work. Light, nimble, plenty of options for hard to reach areas and a superb belt clip. Good onboard storage for bits. It is a bit weak for some types of jobs but paired with the T18 I think there is little to complain about. Both are a bit low in RPM at high gear.
With any of these two as a starting point you might be happy. The CXS is surely not a do-it-all drill, it is too weak. But it is also the only one I would never part with. Mind you the T18 shares charger with the entire 18V platform and the CXS/TXS are the only drills that use that proprietary charger. I don't mind the extra charger for the CXS. It is a specialty driver that hits the sweet spot for me and will stay in the stable regardless of whatever brand passes my fingers.
The CXS only takes up to 10mm drill bits in the chuck. Forget hole saws with the CXS. I have toasted one, almost two CXS machines over the years - and I personally think I didn't push them that hard. They are not brushless and they are not able to withstand too much abuse. For general assembly work they are superb for me though.
The TXS is the sibling of the CXS but I think it is redundant, only marginally smaller than the T18 and as weak as the CXS and the belt clip isn't as nice.
Some people (me included) like the C18 though some loathe the grip. It is very similar in performance to the T18 (virtually identical specs) it has onboard bit storage like the CXS and is powerful enough for most jobs.
The DRC/4 has a better light and is more powerful than the T18, also has a great grip though you need to mod the machine if you want a belt clip that doesn't slip off your person easily. It has four gears and they are all useful but I think they are slightly off for me though sometimes they do hit the sweet spot.
The PDC/4 is a percussion drill, some like it. I don't. They are loud. It is not an impact. Festool does not have an impact in the line up, I sure wish they did.
Of the above drills I own the CXS, the C18, the T18 and the DRC as well as an older T12+3. I use them all. I use the T18 and the CXS the most but on a current job I use the DRC as the main machine and the T18 as a backup and I use the BHC 18 for drilling larger stuff. I also own the DWC2500 drywall gun which I have been very impressed with.