I tried many paddles single keyers and bugs.
Magnetic has no friction , but I would say the rest of the rest of the mechanics are as important.
Some times the shape of the paddles and distances between the paddles matter more as magnetic or springloaded returns.
I now use a Hungarian made single lever key with spring loaded returns, and the man makes springloaded magnetic as Iambic paddles as a couple of single lever keys and I found this single lever I now have the best in comport for my fingers.http://www.amplitec.hu/jani_baratom%20_eng.html
Here you can find my Hungarian single lever key ( number 3), I have the one with the 45 degree angled contact blades, only the contact blades are angled and for the rest of these 2 keys are mechanical identical, and yes you can feel a difference between the one with straight blades and angled ones.
Also used (tested at friends)a few Begali Iambic paddles, Bencher and Schurr and even MFJ paddles.
Also have a few home made Iambic paddle with spring loaded return.
And I used and have several hand keys and I found that one of the most important things for me was form of the knob on the key.
I do not like the flat knobs of the Junker the J37 or Chech army key a lot and I do not like the round knobs of several British WW2 keys. I love the knob of the Swedish postal key.
I cannot say that the magnetic return has big advantages over spring loaded returns.
It is the complete package that makes the difference.
I even think that personal factors are as important.
I find that tight spacing and light use fits me the best