Surfer creates a spherical force-field around himself, and invests all his power into maintaining that force-field; it is then subjected to the following attacks:
1. Cyclops full-blast
2. Vector full-strength blast
3. Mindless hulk punch
4. Angry blast from Thanos
5. Angry blast from Tyrant
6. Blast from Galactus
How would you pit them against Magneto's forcefield? I'm curious, because Magneto is basically a weaker version of surfer, yet his shields are the stuff of legend.
If Surfer's going all out, then yes nothing short of a blast from Galactus should one-shot break the shield.
if he can survive multiple point-blank (lethal intent) blasts and punches from Aegis and Tenebrous, I doubt his shields would fall at the first "angry" blast from Tyrant (I'm intentionally disregarding Thanos even a possibility here).
And that stuff was before Galactus upgraded him.
Anyhow, at the end of the day, anything but the most delicate of blasts from Galactus should destroy his shields, in one go.
I would be surprised if Surfer's shields were, on average, superior to Magneto's.
I get the feeling Surfer puts up shields as much for avoiding having to resort to violence as for the convenience in terms of monologuing time.
some jack-ass minor deity chucks a hammer at him, whilst he's looking his imperious best on his silver surfboard, he just puts up a shield and continues to look cool and speechify on the dire consequences of pissing off his boss and/or the weight of responsibility he feels for his part in the inevitable annihilation of said godling's little universe.
Magneto has his shields up because, it's life or death for him. Surfer, not so much.
I think Tyrant is the one who finally breaks the Surfers full strength force field; if he unleashes the attack on Surfers shield that he unleashed on Thanos, then Surfers shield is going down...
As pertains Magneto, Mindless Hulk overloads him...
mindless hulk as in the one who punched through onslaught would likely break through magneto's shields, but I would bet that blow was above a rabdom angry blast from thanos