Re: Best Convertible for a Generic Kid?
For convertibles, under $100 there is a good recent review of the options on carseatblog.com. I'd check that.
For $100-$150, I'd lean toward seats whose harnesses can be adjusted easily if you're going to be using them with different kids (can't quite tell if you will be though?). Those would be the evenflo triumph 65 and first years/lamaze truefit. (There are some other no-rethread options that normally run over $150, and may sometimes be on sale for less, but these two are consistently under $150.) Other $100-$150 options that are good, especially if used for just one specific kid all the time, are the graco myride and Britax roundabout55.
I probably wouldn't bother listing seats for much above $150 as I would expect most parents wouldn't want to pay that for a daycare seat.
Another thing to consider, if you're using these in your own car, will you be doing the installations? If so then I'd make sure that you are comfortable using whatever seats you suggest. But ideally, from a liability perspective, I'd ask the parents to install the seats in your car (in which case, whatever seats they're comfortable with would probably be best).