http://www.dailywritingtips.com/big-words-make-you-sound-smart-dont-they/ - I think you might find that interesting.
Anyway: Neither are my style. I far prefer Alys to Alix, not sure why. I think I like the look of it better. Tristan has always been too romantic for my style.
Alix, though, is totally usable, as is Tristan. :-D