If your rear rack is going to carry any bags/gear on top it's worth getting a rear rack with lowered rails. They are so convenient for attaching gear and removing panniers without having to take everything off or digging underneath what's tied on the rack. Topeak SuperTourist are decent economical racks. I have a rear rack bag that often stays on the rack and it's much easier to clip panniers on/off with the rack sitting 2" higher. I used to have a Tubus Cargo on the bike and I'd be more inclined to leave the panniers on the bike and dig contents out of the panniers instead of pulling the bags on/off as desired.

http://www.topeak.com/products/Racks...tDXTubularRack

I got an Axiom Journey on sale from REI and was not impressed with how flexible it was compared to the Topeak or Tubus racks. When mounted on the bike I could flex it side to side about 3/4". It looks solid but I'm thinking it's method of attachment allows for more flexing than other racks as it seemed more flexible than the basic old Blackburn rack. I removed it and have used a Tubus Cargo and Topeak ST and the difference is noticable. That said I later got an Axiom Streamliner thinking it would be worth trying on a commuter bike. The attachment with jointed arms was the same as the Journey but it was going to interfere with fender mounts as it sits so low. I replaced the Axiom attachement with plain ss straps. It is a VERY solid rack with the ss straps. I never attached it with the stock mounts so I don't know how big a difference they make. I'm going to attach the Journey on my friends bike with ss straps and see if that's the source of the flexing. The only reason for getting the Streamliner is if you weren't going to put much on the top of the rack but it if I wanted a rack to survive a major crash I bet it would be it.
All of this is splitting hairs but when you have choices, why not?