Nitro Trainers are subject to personal opinion.
Tower trainer is fine if your budget is tight.
I like big because it is more stable in the air and is easier to see.
For that reason I lean toward SIG LT 40 with a 70" wingspan or if you can afford it a SIG Kadet Senior with an 80" wingspan.
Both of these fly very well on an economical .46 size engine
http://www3.towerhobbies.com/cgi-bin...?&I=LXFG19&P=0
http://www3.towerhobbies.com/cgi-bin...?&I=LXBDE9&P=0
(Nitro and Glow are interchangible terms in my neck of the woods )