Springs: Cheap, can replace at any hardware store, easy to pick a custom "resistance" (how much pressure it takes to use the switch).
Magnets: Very smooth switch action, don't wear out or weaken from use, not as easy to replace or customize.
Early mechanicals, especially some of the first clones, were notorious for having poor machining in the switch components which might create a condition where the spring itself is/was part of the circuit (electricity always takes the path of least resistance), giving you a "hot spring" or "hot switch", even burning your finger sometimes if you pressed it not quite the right way. I imagine some very cheap clones still suffer from this problem. Because most magnetic switches never actually allow the magnets to come into complete contact with each other they *can not* be used as part of the circuit (magnets aren't great conductors anyway), meaning that the switch itself must actually be designed to not only work, but work well (without a spring to carry part of the electrical load).
Today $35+ can buy a very nicely machined clone and since the magnets do require some fairly tight machining tolerances to fit (and work) correctly it can be a sort of reassurance, knowing that if the manufacturer bothered to machine the switch to use magnets *and use them well*, that probably the rest of the machine work is of good quality too.
Personally I've found a new fondness for magnets but I have a few mods I use every day that still have springs in the switches too.