Hmm this is a good one, and somthing i have often wondered myself..
I am a techno producer but i have to admit to having engineered quite a few trance tracks fo other people under different names.

i find techno easier to make but i think that is beacause i love it, and i can really feel it and get into the groove. When making trance music im not so into it and therefor not as inspired.

On the other hand i think it had taken me longer to understand how to work techno and learn some of the bizzare 'throw away the manual' production techniques i use to make it. Trance is much more straight up, much less lighter on the processing, but probably more precise..

i think its down to what you love.. if you love something and you have a certain understanding of music production the thing you love will come the easiest..