Everything is a choice thing and in RC it's no different. Instead of the ST try a Thunder Tigre sometime. I no longer use the smaller glow engines. The smallest engine I use is the .91 and those are OS 4s except for one two stroke and that's a SK. Another cheap engine from China and I have only used the .91s so I can't say anything about there other engines. I do have an .80 someone gave me but I haven't tried it yet.
When Saito and OS started getting way too much for there engines they brought them right in line price wise with YS but YS is not for everyone. They are simple, easy and great but too many people buy them and haven't a clue how they work. Not much different but not good for someone that likes to twist screws a lot and doesn't know what the screw does. Most of mine are the 1.20s and they are the old modela without a low end needle. I only have two of the FZ models with the low end needles and they twist backwards to most other engines, They have an air bleed carb.
I no longer buy new glow engines but I do like to trade and I try to only trade for YS and OS. With the new small gas engines glow makes no sense at all if you are buying new. The new 15cc engines are great for 60 size planes plus they cost less to operate and are just a much easier engine all around.
Again, it's all a choice thing. It also depends on what is sold in your local. Here it is Saito and Magnum. I'm the only YS user I know and a few of us use the OS, just a bunch more Saitos but all of them are starting to disapear due to the newer cheaper gas engines.
If you have the money then try them all. Do some trading and you can get engines for next to nothing.