If the electrostaff can stop a lightsaber, I'm sure it could stop a blaster. I'm not sure, though, since they're designed to fight Jedi and not droids, but once it gets to the droideka, it's pretty much done.
IF it gets to the Droideka, you mean. Yeah, I'm sure the weapons could block blaster bolts, but could the droids? I doubt it, Jedi can because of the Force, Magnaguard's don't have the Force.
I think that if the droidekas were superior to the Magnaguards, General Grievous would have chosen to surround himself with them than his 'elite'.
Maybe he choose the Magnaguards because they use melee combat, and he didn't fancy fighting Jedi while Droideka's fought Jedi alongside him. Sure the Jedi couldn't deflect laser bolts back at the Droideka's, to any effect, anyways, but they could deflect them towards Grievous. There are advantages to having bodyguards who use melee weapons.
I actually decided to go with the Droideka's. Anakin could be wrong, after all. But 2 Droideka's made Qui-Gon and TPM Kenobi run, maybe the Jedi would have won eventually, but Qui-Gon seemed to think that it would take more time than it was worth at least. Had it been two Magnaguards? I say they'd have lasted 10, 15 seconds tops against the Jedi. Hell, Kenobi along could have dealt with them and by the time he'd finished, Jinn would have been through the blast door.
In ROTS, Kenobi and Skywalker run from 3 of them, and they pwnd 2 Magnaguards. Hell, later on Kenobi beats 4 at once before fighting Grievous. In The Defense of Kamino, a bunch of Droideka's attack a few ARC's, I can't remember the details but I think it was lke 3 vs. 3, and it was pretty even and then Shaak Ti arrived and helped the last ARC alive of the 3 (Alpha). I say the Droideka's win.