I would like to what is the best OBD1/OBD2 scanner to use with this vehicle?

"Best" depends on who you're talking with. A '91 model is very basic and there isn't a real lot you can do with a scanner. (I consider you lucky. I drive an '88 Grand Caravan simply to avoid all the unnecessary computers, and their problems).

For vehicles of this age range, I have a "Monitor 4000", but those require a plug-in cartridge that covers your car model and year. There are a lot of real nice scanners out there that work on all cars back to the early '80s, and all the way up to current, but those can cost over $10,000.00 in U.S. Dollars. That's four months wages for some of us. A better alternative is to start by looking on eBay Automotive. Next is to visit a repair shop and see if they have people who show up once a week with a tool truck. Those guys will often have professional scanners that were traded in for a newer model. You also might inquire at some shops to see if they have an old scanner they'd like to sell. This equipment becomes obsolete real fast, especially the older ones that can't be updated easily. If you can find a scanner that is updated with new cartridges, the manufacturers will be all done producing the latest updates, so you can find one for your car and stick with it.

Don't get a simple code reader. A regular scanner will display sensor values while you're driving, and they are "bi-directional", meaning you can command the Engine Computer to do things like turn on the radiator fan or fire an injector so you can troubleshoot those various circuits and see if they're working.