Hi T.,
I'm a Child Passenger Safety Technician and quite familiar with all the convertible child seats available for sale in the US right now.
What's important to keep in mind is that there is no one 'right' or 'best' seat and that what another person loves may be awful for your situation. You know, if you're a size 32B and someone loves her 36D bra, it doesn't necessarily mean it's a good choice for you too ;-)
The 'best' car seat
1. Fits your child
2. Fits your car
3. Fits your budget
4. Will be used correctly EACH and EVERY time you ride in the car with your child.
That being said, the new Alpha Omegas (the ones that forward facing harness to 50 instead of 40) are decent seats. They make TERRIBLE UNSAFE boosters, so if you are buying it because it converts to a booster, don't let that be part of your decision. (If you want more information on boosters, let me know)
When looking for a convertible, keep in mind the most important thing is that it should allow rearfacing for as long as possible. You might have heard the old rule that once the child is 1 year and 20 lbs she can forward face in the car. We now know that to be patently false, and causes a FIVE HUNDRED PER CENT increase in death and injury in children under 24 months. Two years should be the absolute minimum your child is before turning forward facing.
Seats that will allow you maximum rearfacing time AND will last forward facing until five years or so (when most kids are old enough to move from a harnessed seat to a booster) are, in order of price
Evenflo Triumph Advance (140-180)
Graco MyRide65 (rearfaces to 40 lbs) (150)
Cosco Alpha Omega Elite (150-180)
Britax Roundabout50 (NOT THE ORIGINAL ROUNDABOUT) 170
The First Years True Fit (170-190)
Sunshine Kids Radian65/80/XT (220-280)
The Firs Years True Fit ARB (270)
Britax Marathon/Boulevard (270-330)
Any one of those seats is a decent seat, and all of them have pluses or minuses. Pick the one in your budget that you are comfortable using, make an appointment with a Child Passenger Safety Technician for an installation and education session, and you can't go wrong, as long as you rearface to the limits of the seat!