Update: As someone pointed out, I am not a "car" person. This will be the first car that I truly buy on my own. Like I said, I have about $15000 I can drop (I was saving to buy a motorcycle and a new tv but my car issues killed that). I'm currently in my rotations for Med school and have another year of that before I start residency. Don't really want car payments when I get my school loan money in one lump sum (pretty much what I'd be using to pay for it).
I am currently (this hour anyway) leaning towards certified preowned or something of the sort. I am weary of preowned in general and hoped to avoid used car salesmen completely. So the cert preowned seems like a good option. With Pres Day coming up, I was hoping to spend some time researching and then take advantage of whatever is being thrown at me then. I am overall hoping for something with Decent Gas Mileage and Not a ton of headaches with enough room for like 4 people. I keep hearing suggestions from Friends/Family to look into small SUV's like the Honda CRV, but to be honest, I don't know how much their opinion is really worth.
Pretty much any help/suggestion is appreciated.
Tip on used car salesmen... you hold the money, you have the power. If you don't like who you are dealing with, get up and get out. I REALLY REALLY mean that. If you're looking at a car that BB's for 13 and they list it at 15, ask once or twice as needed to buy it outright for 12 cash. If they haggle or BS you too much, get up and leave. There is always some car dealer somewhere that actually wants you to buy his car, and will take the fair amount for it.
Secondly, as other have pointed out, if you buy new, you are paying for depreciation as soon as you drive it off the lot. In other words, if the MSRP was $15k new, and you drive it off the lot, the value is now $11k if you're lucky. You can avoid that buying a gently used car. My wife had gotten hers with under 20k miles, and I bought my vehicle with about 30k miles. Never had any problems with either of them for quite some time.
As for make and model, just look at what you like, test drive a few, and do research on what you like. If you want a compact sedan or a full-sized sedan, it all will depend. If you're an averaged sized person (6' or less, 200lb or so) you'll probably fit in about anything you look at. If you are taller, you might start running into issues with smaller cars. Problems like knees in the dash, head on the ceiling, crammed up against the steering wheel because the seat doesn't go back far enough, etc.
But seriously, with 15k in your pocket, you have all the power. You're not looking for them to write you a loan, and they'll be pleased as punch to have that money come straight in that day. If they haggle too much for your liking... LEAVE.