RE: Best All Around Engine?
If you fly pattern ,you need lots of smooth power.A weedwacker aint going to give you that.A good gas engine in the 40-50cc range will cost you between 4-700$
Often the exhaust can add a bunch too (like a tuned pipe and such)
If you are going to go for cheap,then I would suggest the Chinese DL50 (about 400),but its loud on stock exhaust,and is an entry level motor.many have had good sucess and there is service in the US.
I'd suggest saving another couple hundred and get a proven motor if you plan on flying it for a decade or more.
Browse thru this gas engine forum and do a bunch of reading.You will quickly get familiar with names and issues of certain brands.Spend a few evenings here.Its impossible to sum it all up with one reply.