My first plane was a Superstar 60 which was a very stable and eay to fly trainer. This plane appeared to fly at a similar speed to the average 40 sized trainer but was easier to see in the air and was probably more stable in wind.
I also briefly had a Hobbistar 60 MKIII. I can't really comment on this from experience as I crashed it on the 2nd flight (maybe that says it all).
The trainer that I actually soloed on was an LT-40. Although this uses a 40 sized engine, it is the same size as most 60 sized trainers. It is built lighter enabling it to use the smaller engine. The larger wing area for the weight enables it to fly a lot slower than many other trainers making it easier to learn on.