Hard to Pick
Like others have mentioned, it really depends on how you plan on using your Jeep. If you plan to take it off-road occasionly, and do moderate to easy runs, then get the sport. The Jeep sport is incredible. You'd be surprised what it can do just stock. If you plan to do a little more aggresive stuff, get it raised and put bigger tires on it. Now, if you plan to do some major rock crawling, the Rubi is the way to go.
Some Rubi owners will get upset by what I am going to say here. Many Rubi owners buy that Jeep for status, "It's the best". Not true. It really depends on what you want to do with your Jeep.
The Rubi has the 4:1 transfer case. That is much better than the Sport. When going down a hill, you usually won't have to touch your brakes if you have it in 4 Lo. The Rubi has a D44 front diff vs the D30 on the Sport. I get tired of hearing this is such a pro for the Rubi. They both use the same housing and the tube and wall thickness are the same. The only difference are the center section and the stock spline count. If you plan on building up this area, then the D44 is better due to the spline count.
The Rubi has lockers - these are great, especially if you are rock crawling or going over shale, or other very tough areas. You can put lockers on your Sport if needed. The Rubi has the e-diff (electronic sway bar disconnect). That is a nice feature if you need some major articulation. And it is a push of the switch. However, I know many Rubi owners that have had to replace the electronics once it has gotten wet. If it goes after warranty, you're looking at some major dollars to replace. If you really need a disconnect, you can put a manual one on your Sport. You have to go under you Jeep and disconnect but how often are you going to do this or will you ever need it?
The Rubi has 4.10 gears. These are nice, especially if you plan on lifting and going with 35" tires or larger. If you go really large, even the 4.10 gear will have to be changed out. However, the Sport has either 3.21's or 3.73's. Great gearing for on the road. If you plan on a little towing and some medium off-roading, possibly lifting your Jeep and putting on 33's, go with the 3.73 gears.
The bottom line is, figure out how much and how tough your wheeling is going to be. For some tough wheeling Jeepers, they get the bare minimum Sport and build from there, replacing diffs, and everything - major major dollars for this. Others that do recreation off-roading, go for the Sport or Sahara (nicer options and interior) and lift it and put on wheels and possibly some lockers, bumpers, and a winch. Others that really go to major rock crawls go for the Rubi.
They are all great off-roaders.