I have the XYZ 50 and so far am very impressed with it.
It's in a Nitroplanes Yak 54 50cc sized beasty, and while vertical is not out of site, it does haul it with authority.
Right out of the box, installed onto the Yak (But with no Cowl installed for easy tuning) I flipped it full choke etc until it popped, closed everything and opened the choke and it fired up first flip.
I'm using a 2800mah 6v NiMh pack on the ignition. I'm also turning an APC 20x10 using 32:1 oil mix.
They're also working on a 50cc HP (High Power version) they say will retail a little over $300 but they have not released it yet.
This is just my opinion on an engine I have used. I have not used any of the others so cannot comment on any of them.
George
ORIGINAL: kahn41
Yes I could... but the XYZ 50 is 259.00 compared to well over 300.00 for the others. Another contributing factor is how good are they? how do they run? against the other 3