There really isn't a "best" mag. Slicks are readily available and light weight. Since Champion bought them, they are now also incredibly expensive. Also, they get a 500 hr inspection, then recommended tossing them at 1000 hours, although I have run them well beyond that. They are not economically viable for magneto shops to overhaul, so at 1000 hrs, it is recommended to buy new replacements.
The newer 4300 series Bendix mags are good now that they finally seem to have all the impulse issues sorted out, but also pricy and a bit heavier than Slicks. But they can be overhauled over and over rather than tossing them at 1000 hrs.
The Eisemann mags are my favorites for old engines. Really solid mags with NOS parts still available. The AM4s are unshielded, which can be an issue. The LA-4s are shielded and really good units, but it's hard to find a set or right hand LA-4s. Also getting to be difficult to find shops to overhaul them.
The old Bendix Scintilla SF4RNs are also rugged old mags. They are large and heavy. NOS parts are still available, although overhaul shops to work on them are getting to be challenging to find, but are still out there.
Any of these mags will provide a good spark at the right time, which is really all that's required of them. Each has good and bad qualities, so weigh them for yourself and use the one that suits you best. Nothing wrong with any of them.
-CubBuilder