The Trans Pack isn't a BP as mentioned before, The main benefeit from the Trans Pack is its compactness, but for rock solid stability the BP is the way to go.
As mentioned before you may want or not the STA.
IMHO, the main advantage of the STA is that it separates the tank from the diver just enough so the divers head doesn't hit the 1rst stage (a common complaint of Trans Pack users since the tank sits next to the body of the diver), added weight and a bit more stability is a bonus.
With a BP with the Single Tank camband slots, the tank may not hit the divers head due to clearance offered by the rib in the center BP, so in most cases, STA may not be needed for clearance.
If you want Dive Rite gear, you may want to check
www.diveriteexpress.com for competitve prices and super fast shipping not to mention great service.
Also DSS gear has many innovations that are worth looking into for first time buyers
www.deepseasupply.com
Any way, look at the top manufacturers and decide what's best for you, here are a few:
www.diverite.com
www.omsdive.com
www.hammerheadscuba.com
www.oxycheq.com
www.halcyon.net
www.zeagle.com
Decide what you want and then shop around for the best price, or better yet start another thread (war) here on SB to have the opinions of other divers.
Enjoy the process of selecting your gear, it's very fun..............