Only thing you need to know (mag ones or 'suction cups') is what is your car/jeep made of. My old Liberty is solid steel so I have the double Mag one's and never (well, on the rare occasion) take the things off.Call Poppy at the Red Shed, he carries the good stuff. Get the magnetized ones, they are bomber and I've used mine many days driving up and down the Clearwater and recently the Thompson.
I've got a pair of those and like 'em, but if you are going to rack them up with a spey reel, you need to buy their spacer to increase the height so the reel is off your hood. I made one on my lathe and that solved the problem.