I also really like the Safety 1st and Cosco boosters.
Yeah, they require vehicle head support, but so do backless boosters and that doesn't stop me from recommending those.
Besides, I don't really believe that the seats that don't require support actually offer more protection; it's a matter of whether the manufacturer chooses to make it a requirement or just let people maintain the illusion of whiplash protection. Unless you're getting something really structurally sound, such as an Oobr, you really should be putting head support behind your child if at all possible. If it simply isn't possible, I would of course choose a seat that doesn't require it, because at least then you're not going against the instructions.
In a situation where you have to remove the head rest to make a HBB fit, then I would sooner use a backless booster and leave the vehicle head restraint in place.