I would suggest trying them both out at a store. I really liked the TXS and thought it was an extension of my hand and the CXS not as much. Both are nice drills, though. Great balance, ergonomics and handy.
I have both and really like both of them. I bought the CXS a few years before the TXS was available. I also have a T18+3 (my fist Festool drill), three Milwaukee’s, and two DeWalts.
I would still buy the CXS first if I had to do it over again.
I own both. Got the CXS first, then the TXS. Initially I liked the T handle more, after a couple of years I've decided the prefer the CXS. As others have suggested, if possible, try them both before you buy.
Like Runhard, I bought the CSX before the TSX was out. I did later buy the TSX and ended up preferring it. The CSX seems to get into tight spots better than the CSX. The TSX feels better in my hand better than the CSX. Both are great drills. If possible, handle both before buying.
I tried the CXS and the TXS. The TXS fit my hand better--the CXS felt a little cramped to me. So I chose the TSX. And the T18... Definitely try them both before you choose.