Comparing a magnetic mount to a permanent mount will show that the mag mounts have a bit additional loss.
The capacitive coupling used for the ground plane connection on the mag mounts doesn't come free.
While the difference is slight, if you really are looking for the best install, then it's worth the permanent NMO mount in the dead center of the roof. Not only does this provide a direct connection to the ground plane, but it also often results in shorter cable runs, which can remove a little bit of feed line loss. It also prevents the cable getting pinched, crimped, damaged, or water intrusion when you try to run it through a window or door.
All these little losses add up after a while.
And I'll second the Larsen NMO-27 installed on a permanent mount NMO in the center of the cab. Short of a full 1/4 wave 108" whip, it's an ideal solution.
There is no magic pixy dust that makes one brand antenna work better than another. Antenna performance is governed by the law of physics. Those laws cannot be cheated by snake oil, clever sales tactics or magic voodoo waves. What you want to look for is a quality built antenna that is designed for the frequencies you are using.
The nice thing about NMO mounts is that they are the de-facto industry standard on the professional side. If installed correctly and properly maintained, they'll easily outlast the vehicle. There's a good reason why nearly every single fire truck, police car, state trooper, sheriff, ambulance, etc. will have antennas permanently installed with NMO mounts with a proper ground plane underneath them. That's because when lives are on the line and radios absolutely need to work, you don't go with magnets, stick on, funky brackets, voodoo magic, etc. If that stuff worked, you'd see every public safety vehicle using it.
The Larsen brand antennas are excellent performers. Larsen has been building high quality, professional mobile antennas for decades. They have an excellent reputation and stand behind their products. I've got Larsen antennas that I'm running that are well over 20 years old.
If you want professional results, then use professional products. Avoid anything you find at a truck stop, Radio Shack,etc. While it'll cost a bit more, it'll last a lot longer and it'll work much better.