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I've done everything from self guided adaptive optics sbig cameras through to a humble 50mm finder with a Qhy5, I've used an ST80, zs71, I've used camera lenses as guide scopes too. By far, no exceptions, OAG (and self guided/AO) setups work the best. I think self guided with ao had the edge, but with a good quality OAG and a sensitive guider like a qhy5 2 or a Lodestar beats self guiding without AO. The reason I say this is because with my st10xme that I used to have, the imaging sensor had 6.3um pixels and the guider had 7.4um. The difference is slight, but I noticed when going to a guider with 3.7um pixels I found guiding to be more accurate. Could have just been in my head.
Using an st80 was nothing but heartache. Guide rings that flexed, the focuser was wobbly as all get up. I ended up needing 3 rings, 2 solid rings to mount the tube and a small guide ring securing the focuser drawtube. I still think there was a margin of flex in the rings somewhere because I went from that to a solid mounted zs71 piggyback on my tmb80/480 and that provided very good results but when I planked a 2.5kg camera on the back of the TMB guiding went up the wazoo again. I moved to an OAG and never looked back.
Now I'm using a finder guider but it is solidly mounted to the imaging dovetail through a home made bracket, and I'm imaging at 300mm focal length so I assume when I get it running it will be fine. Only reason I'm not using an OAG for this is because it's a dslr lens on a dslr.. 0 available backfocus.
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