Hi - My daughter is just getting to that staget as well and I just did my research on this topic. We have a Consumer Reports membership, so I looked up the top rated boosters on their site and here is what I found. Based on what I read and the ratings (both Consumer Reports ratings as well as the parent ratings on their site), the backless boosters rate better overall, and most importantly with respect to crash ratings. We are going with the Graco Backless Turbobooster. Considering we told ourselves money is (mostly) no object, I was surprised to find that the most highly rated booster was only $20 and could be bought at Target, or Babies/Toys R Us or even Walmart.
Here are the ratings for the top Booster Seats. I am entering them in the following sequence: Brand & Model, Approx. Retail, Overall Score (out of 100), Crash Rating, Ease of Use, Fit to Vehicle (the last three are coded as E=Excellent, VG = Very Good, G=Good, F=Fair, P=Poor)
High Back Boosters:
Graco Turbobooster 8493, $50, 82, VG, E, E
Recaro Start, $350, 80, VG, E, E
Compass B500, $70, 78, VG, E, E
LaRoche Grizzly Bear Booster, $115, 74, VG, VG, VG
Cosco Protek, $35, 74, E, F, VG
No Back Boosters:
Graco Backless Turbobooster, $20, 92, E, E, E
Cosco HighRise Booster, $15, 84, E, VG, E
By the way, it is NOT true that only a High-Back Booster is safe for your child. If you read the NTSA website on the topic of boosters, you will find that all are safety tested to a minimum standard and that the key differentiator is EASE OF USE/INSTALLABILITY...to make sure it is positioned correctly FOR YOUR CAR. Here is the link to the specific NTSA info on boosters : http://www.nhtsa.dot.gov/portal/site/nhtsa/template.MAXIM...
Here is the link to the ratings...Please don't just look at the # of stars, but read the actual rating page for that item. You will find the comments MUCH more helpful than the stars and in some cases, the stars don't jive with the comments. This is the case with the Turbobooster for example and why I am still going to go with that seat for my vehicle. http://www.nhtsa.dot.gov/portal/nhtsa_eou/info.jsp?type=all
I would suggest cross referencing these and the Consumer Reports ratings, which is what I did in selecting my booster.
Hope that helps!