We bought the britax regent when my son was 2 1/2. We also had the britax boulevard. The regent is what he now uses. It's AWESOME but HUGE! I love it and love that it will be the last carseat he'll ever need. The downside is that it's not very portable because it's so big. It fits in my Honda Pilot, but it wouldn't fit in a small car and I wouldn't move it between vehicles much.
It wouldn't fit in my husband's 2 door sportscar (nothing would), so I talked to the online customer support at www.elitecarseats.com and they suggested the Safeguard Go for us. I LOVE THAT WEBSITE! We bought the Safeguard Go (new on ebay) for my husband's car and it's pretty awesome too. Not as bulky/protective/comfy as the Regent, but it's like a booster seat with 5 point harness and LATCH. It has a removable back as your child gets older and folds up into a little bag for travel. The downside is that you have to have an upper tether hook in your car for the flexible back to hook onto. My son usually travels in my car, so the Go is only occasionally used.
Hope this helps! Happy shopping.