G'day
I'd suggest the Sig Kadet LT-40. It is big, light, flies really well and does not need a large expensive engine. My mate is flying one with an OS LA 46 and it is perfect.
There are many smaller, faster, Asian made trainers very few are as good as the Sig Kadet LT-40. You can get them direct from Sig or your local hobby shop may have one.
www.sigmfg.com
It is not cheap but it is worth the extra. I am currently building the kit version. So far I have managed only to trim the wing ribs ready to start on the wing.
An alternative for half the price (plus freight) is from the well known Hong Kong web based RC seller. They are selling an ARF version of the Sig Kadet Seniorita. It is not the "genuine" Sig version but it looks exactly the same to me. I have just bought one. It is sold as an electric and mine may well end up that way but it would be easy to put an OS LA 25 or similar in it. I used to fly one with a PAW 15 diesel. They do not need much in the engine department. But, they do fly really well and very slowly if required.
Have fun choosing.
Mike in Oz