I'm VP of Membership for a fairly good size club. At my club we use a LT40 and Kadet Senior every Tuesday on training nights and both have old, beat, OS Max 40 size engines. They are fine for learning to fly and are plenty capable at taking off and flying . They are extremely reliable at starting and not quiting unless run out of fuel. On the other hand the most popular choice for new members flying the LT40 is the OS Max 46AX. Based on your choices, I would save the money and go with the 40 size engine. The 46AX is more powerful, no doubt, but for training it REALLY isn't necessary and is more prone to quitting and deadsticking in my experience. I've heard countless times about an AX deadsticking, and mine did as well until really broken in. Don't know about the TT but I'd still recommend saving the money and going with the weaker engine to train with. Weaker is just a relative term. The 40 is more than capable at training, again, from experience. Once you have had the plane for a while and get into a new plane, you'll always be able to go back to the trainer and upgrade the engine to a larger four stroke RATHER than a 46 two stroke and will enjoy your trainer in a new way with more experience. Just my two cents, again, from seeing MANY other members personal experiences who have done just that.