Information again taken from babycenter.com
Britax Frontier For children over 2 years of age and harnesses to 80 lbs. Top slots are 18 inches. Tether not required, but recommended. Harness height is adjusted on back of seat, but there’s no rethreading of harness required. Has a flexible LATCH strap with typical Britax push-on connectors. LATCH may be used when seat is in booster mode. Has 3 crotch strap positions. Nice padding. A 9 year expiration. Deep cupholders that can disappear into the side of the seat when not used. Can be installed with the seat belt using the short belt path or long belt path. FAA approved when used with harness. Converts to a good booster with no weight limit. Replaces the Parkway and Monarch. Retails for $279.
Cosco/Safety 1st Apex Harnesses to 65 lbs, then becomes a booster to 100 lbs. Top slots are 17 inches high. Requires adjustable headrest or a very tall vehicle seatback behind it for support. Then becomes a very nice BUT VERY WIDE booster that doesn’t fit small children well. This seat is outgrown totally when the tips of the child’s ears reach the top of the vehicle seatback. (Fully extended it has a back height of 32.5” tall) FAA approved when used with harness. The new blue/black and all the brown ones have EPP foam in the headrest. Retails for $99-150.
Graco Nautilus 20-65 lbs for harness, then becomes a booster to 100 lbs. Top slots are 18” high. Converts to a high back booster similar to the TurboBooster, and can also convert to a backless booster. 30-100 lbs weight limits in booster mode. Booster shoulder belt guide is at about 20"; might be slightly taller than the regular Turbo. 19 inches at the widest point (the base) and 13 inches deep. FAA approved when used with harness. Built-in cupholder and side pockets in the armrests. The base has two settings and can be slightly reclined. LATCH limit of 48lbs, does not allow for LATCH or top tether use in booster mode. Life span of 6yrs. Priced around $150.
Britax Regent (used to be Husky) KING of car seats is right! Harnesses to 80 lbs. Top slots are 20 inches. Requires a top tether after child is 40 lbs. (unless using a lap-only belt, then it’s required at 50 lbs.), but a tether should really be used all the time. Retails for $220-$260. Not good for children under 2yo.