The difference is in the mounting. I have Yakima Blacktop pro 16 and believe it have the best mounting system that never require you to disassemble anything. Thule use "U" bolt clamp that stil need to be removed but does not need any tool. The Sears one are the bulkiest and need tools to remove the "U" bolt.
Thule, Sears and Karrire are basically made by the same company (Thule) but marketted to different market.

Depend on your usage Sears might be the best for big luggage although they dont have any tie down point inside so you would need to stuff it or have very good padding. Yakima and Thule are geared more for sport so they could fit Ski, snowboard, paddle or any long sport gear.

Thule have the best look but its exaclty the same as Sears exepct its fatter. If you just need to carry Luggage and does not need to take it on and off I would go with Sears since the price are right.