I'm building one now and I settled on a Saito 100. I think it is the best combination of power and weight. The other engine I was looking at was the Saito 125 it's lighter than the Saito 120 by a good bit and 4 oz more than the 100. But I'm not looking to 3D or send it to the moon...
I'm building with the goal to keep it as light as possible. I think that's the main problem with the kit. People think it's a bigger plane than it really is and try to cram a bunch of larger stuff in it.
Here is a great build thread. Lot's of debate on different gear.
http://www.rcuniverse.com/forum/m_38...tm.htm#3823449