I agree with the previous poster; while there have been some great improvements in 3-in-1 seats lately (this new Symphony, the updated Alpha Omega Elite that harnesses to 50 pounds instead of 40, and has taller top slots than the regular AOE),
but the improvements still aren't enough for many kids. Here's my reasoning:
*the Symphony has good rear-facing capabilities (we want kids rear-facing to at least age 2, preferably longer, until the rear-facing limits have been met), but it falls short forward-facing harnessed due to a 40 pound harnessed weight limit. Many children reach 40 pounds at 2-4 years old and are simply not mature enough to stay seated properly in a belt positioning booster seat using the vehicle seatbelt. Since there are many options to harness beyond 40 pounds these days, the Symphony's forward-facing harnessed weight limit is a disappointment.
*the new Alpha Omega Elite has two major improvements over the regular Alpha Omega Elite/other Cosco/Safety 1st/Eddie Bauer 3-in-1s: a 50 pound forward-facing harnessed weight limit instead of the usual 40 pounds, and a top harness slot position of 17+ inches, which is a harness height that should actually get kids to 50 pounds, or close to it, without getting too tall first. The older-style 3-in-1s had a top harness position of 15ish inches, and many kids got too tall for that seat even before 40 pounds (my own included). The AOE has great rear-facing capabilities, and the newer ones have those taller top slots and higher weight limit, which is awesome, but these seats fall short in booster mode. Their design just doesn't position the seatbelt optimally on many children, allowing the lapbelt to ride too high on the abdomen.
For a baby who's soon-to-outgrow the infant seat, I'd focus on a convertible seat (one that rear-faces and forward-faces) that has a high (33-35 pound) rear-facing weight limit, tall seat shell (so kiddo doesn't get too tall to rear-face before getting close to or reaching the RF weight limit), a high (50+ pound) forward-facing weight limit, and tall (17+) inch top harness slot height. The Britax Marathon/Decathlon/Boulevard, First Years True Fit, and Evenflo Triumph Advance are all great choices. The new Alpha Omega Elite with 50 pound weight limit is also a good choice, as long as you know you'll probably want a dedicated belt positioning booster once the harness is outgrown.
You could also save a bit of money in the short term and go with a seat like the Safety 1st Uptown or Avenue (mostly the same seat, Uptown has a bit more padding/less shoulder room and a more plush cover, Avenue has cuter print covers, more shoulder room). It has great rear-facing capabilities (nice, tall seat shell and 35 pound RF weight limit), a 40 pound FF weight limit and 16 inch top slots (a good height for a 40 pound seat, most kids will have no problem reaching the full weight limit with 16 inch top slots). The downside of saving money now and going with a 40 pound weight limit seat is that you'll probably want/need to get another harnessed seat once the 40 pound seat is outgrown in order to get your child to a mature enough age to use a booster seat. The good news is, there are some great higher weight limit combination seat (forward-facing-only harness, converts to belt positioning booster) options right now (Graco Nautilus, Britax Frontier). And, by the time your little one needs to be forward-facing, there will be lots of other cool choices.
So, my advice is to focus on a great convertible to keep your baby rear-facing for a couple more years, and worry about boostering when he's about 5.