My thoughts...

You say that you're not tall enough to ride the "Large" Giant, and the fact that Giant doesn't come in Large for women does present a problem. BUT...have you considered looking at the "Medium/Large" men's Giant Defy frame? I believe the Defy is the men's version of the Avail. Just something else to consider.

Also...you mentioned SRAM Rival being on one of the bikes you are considering. Like Shimano components, SRAM has a hierarchy to their component groups. Shimano's higher-end groupset from lowest to highest (in terms of quality and price) are - 105, Ultegra, Dura-Ace. SRAM's are - Rival, Force, Red. So...in terms of better components...I'd say the Fem 3 with the Ultegra group would be a bit better than the Fem 4 with Rival. But that's just my opinion. I'm currently riding a bike equipped with full Ultegra SL components, and it's great...but I'm fairly certain that my next bike (whatever that may be) will have SRAM Force (or Red if I can afford it) since I'm hearing that the Force groupset has been totally revamped for 2010 and is getting glowing reviews from everyone.