Go with poly -- it is more durable and slightly more yellow than acrylic, but takes longer to dry.
I would get at least 3 coats.
Make sure they wait 24 hours between coats and that they buff and use a tack cloth between coats. They should use a new mop to apply each coat. It is not worth saving a few dollars by re-using the applicator mop, when there is a risk of adding dirt or creating bubbles in the finish. I recently found out the hard way and had to threaten legal action to get them to correct the problems from being sloppy and cheap. It wasn't pleasant, I've never had to make such a threat, and I hope I never have to do it again!
Get them to apply filler to the parts of your floor that need it (if any.)
Don't make your final payment until after the last coat has dried and you are happy with the result! I paid after the last coat was applied -- a big mistake!