1) Does anyone have any ideas about reasonably priced companies?
I would check out the Tanzania Association of Tour Operators for a list of reputable, local tour companies. You can try contacting them before you arrive, or just booking once you get there if you have a few days to spare. Personally, I used a company called Comfort Safaris and had a great experience, but I have heard good things about a number of different operators as well.
2) If you had to pick one over another which would you recommend?
If you are talking about picking between Ngorongoro, Lake Manyara, and Serengeti, I wouldn't pick any over the other. I would do a 5 day safari of all of them. I did 1 day in Manyara, 3 days in Serengeti and 1 day in Ngorongoro. I think 5 days is perfect. Less than that, and you might not get a chance to see as much of the animals as you can, more than that, and your ass will be sore from bumpy roads and bad shocks.
The safari is, in retrospect, one of the greatest travel experiences I have EVER had, so I would always suggest to people to spend money to do the safari and if you have to, cut other stuff out of your budget.
Greg