I have a Hyundai Santa Fe which fits three across in the back. I did get a new car seat which was a little narrower but still highly rated for my middle child rather than a new car. Right now I have a high back booster, infant carseat, and a Sunshine Radian 65 across the back. No problem whatsoever getting them to fit. When you are looking at cars, look at the hip room measurement (available online) for the back seat and compare that to the widths of all your carseats. I use my car for mostly around town and we mostly use my husband's for longer trips, although I have had the kids in mine for hour plus trips with no complaints about being crowded or anything. And it is nice that the older kids can easily hand the baby a toy or whatever she needs.
My husband has a GMC Acadia which has a third row with two captain's chairs in the middle. Like a minivan easy to climb in and out of the third row that way but we like the drive and look and feel better than a minivan. My only complaint with the Acadia is there is very little room in the backend behind the third row. Although, that being said, we rent a house with our in-laws every summer and had no problem making everything fit in the backend or next to my son in the third row. We had the stroller, pack and play, bouncy seat, all the suitcases, toys for the kids, beach gear, etc. We can easily fit an adult in the third row with my son comfortably. We can also fit two non-carseat kids back there with him or one more carseat kid. We could not fit three carseats in the third row.
We did look at the Santa Fe and the RAV4 with third row -- the third row did not have any legroom. I could not sit back there at all.