upgrade from stock turbo

Best is a pretty vague term. If you are running the stock injectors, your money is better spent upgrading them, the fuel system and the chip if you are on a stock ecu. Next is the converter. A good converter is worth what you pay for it.
The turbo is just one part of a pretty big bunch of parts.
Max out the stock turbo you might like it, its good for 360 hp
But your fuel system isnt, after thats addressed the next logical step would be a ta49 with no converter change, if you just start throwing bigger turbos on the stock stuff things get wonky.
You gotta do everything else that goes with a bigger turbo. I ran my stock turbo at 22 psi with alky and 80# injectors. It can run great. If you don’t wanna do injectors and a Hotwire and whatnot, stock turbo is your best bet. Like previously mentioned, if it needs rebuilding, get it rebuilt
I see you're looking for a Stock Turbo in the parts wanted section. A used one is always a crap shoot.

Why not just have Bison or one of the other turbo builders here go thru and freshen yours up?