You'll be better off with the SIg Kadet LT 40. Mainly because it is more common than most trainers out there, so you'll get loads of help (and advice!!) and I beleive it's been re-vamped recently..

.40 sized aircraft are just easier... easier & cheaper to build, transport, fix, fly, etc. Granted, the larger bird will fly slightly better, better in winds, and can bee seen easier..But what ever teh choice, you cannot go wrong with either Sig Or Great planes! especially for first time builds!