I know a lot of people rave about the Britex (I can't help but wonder how much of that is due to people's instinct to feel more expensive must be better...), but I have the Evenflo Triumph Advanced and I love it!!
Don't let the size scare you, they all look pretty huge when you first see them compared to the infant seats, but I dont think the Evenflo is really any bigger. It fits fine in the back of my little Mazda3 - facing back it did only fit in the middle, but forward facing it is much easier and fits with plenty of room in any position.
Some of the features I love about the Evenflo:
1. Not only do you not have to rethread the sholder straps, but you can move them up and down each time you position your child in the seat so you know they're just right.
2. The side knob adjustment of the strap tension is the BEST! So much easier than trying to pull that strap out between the legs (especially if you encounter a kicking screaming toddler once in a while) - the release takes a couple trys to learn but once you get it you'll be doing it without any thought at all. Super easy adjustment means that you will actually adjust it just right everytime, as they are intended to be, instead of just assuming 'it fit ok last time I put him in, so it'll fit this time...' - It doesn't matter how safe or well rated a carseat is if you don't use it properly.
3. The one I have, 'Premier' edition I think, has a super plush seat and easy release LATCH hooks, which I didn't think would be that big of a deal, but when you're taking it in and out to move it (or to vacuum up all the assorted cheerio's and crumbs), it makes it soooo easy.
4. I has very high weight/hight limits.
5. $, sooo much cheaper.
Sorry this was so long but I just had to share how much I love this seat. Hope it helps!