I bought one of the universal Bosch o2 sensors. Would it be better to solder the wires of the old connector to the new sensor or use the Bosch Posi-Lock set-up?

Either would work but I think it would be nice to have the OEM look and convenience of having the quick disconnect plug. Plus soldering under there doesn't sound fun.

There is a guy on ebay that sells OEM direct replacements for a lot of cars. I just bought one for my 90 legacy. I will let everyone know how it works when I get it.

I bought one of the universal Bosch o2 sensors. Would it be better to solder the wires of the old connector to the new sensor or use the Bosch Posi-Lock set-up?

That's exactly what I have on my 2.2L right now. With the kind of low voltage value associated with an 02 sensor, I think you need the best connection possible and that's solder. Easy to do also: I cut the wire at the old sensor to make removal easier (if you have a 2.2L you just bend over the right fender with an open wrench and go at it) and made the splice on the kitchen table with my soldering iron and heat shrinkable wire covers. No problem reinstalling the new sensor with the new pigtail on when you use an open wrench from above. Just reconnect and you're in business.

Good luck!