Stick with the Britax Marathon or Fisher Price Safe Voyage Deluxe.
I've used and measured all those seats you mentioned. B/t all the carseats everyone in my family uses for the 3 grandkids, we collectively own a Triumph, Comfort Sport, Cosco Alpha Omega Elite, Fisher Price Safe Voyage Deluxe, Britax Decathlon, and an Evenflo Tribute.
Skip the Triumph, Comfort Sport, and Cosco/Eddie Bauer 3 in 1 for all the reasons given by other posters. In addition, the Eddie Bauer/Cosco Alpha Omega (3 in 1) is the *same height* as the Britax/Fisher Price...but they have top harness slots over 1.5" inch higher than the Eddie Bauer and harness to 65/55 lbs., instead of only 40. Since most kids outgrow seats by height before weight, they will last the same amount of time as the Eddie Bauer, but your child will be much more safe, b/c she will still be in the harness! For the same price or only $30-50 more, you'll get longer harnessing and ease of use out of the Britax/Fisher Price.
You definitely want to skip seats that only rearface to 30 lbs--your baby already weighs almost 19 lbs....and it is recommended that infants and toddlers rearface to at least 18-24 mos. and over 30 lbs....they are 4 times more likely to break their neck in an accident if they are forward facing sooner than this.
If you really don't have the $$ right now or prefer to choose one of these seats later for whatever reason, I'd suggest looking at the Safety First Uptown for $80-100.
You can order it online and some Wal Marts have it in stock. It is plush, has EPS foam, rearfaces to 35 lbs., and forward faces to 40 lbs. It also has nice, tall harness slots.
hths
henrietta