David Lee Roth is a funny, charismatic lead man who unfortunately doesn't understand there are times when the "Diamond Dave" act needs to be left on the stage.
Eddie Van Halen is a drug-addled, egotistical nutcase who thinks that because the name of the band is his last name, and because he has the most instrumental virtuoso cred of anybody in the band, and because he used to be the most mainstream celebrity in the band (hell, he married Barbara Cooper from One Day at a Time... schwing!), that his own diva behavior is cool whereas DLR's diva behavior sucks.
I'd argue you could subtract Alex Van Halen from the band without changing their sound too much (though I think he's a great drummer and a good fit for the band), whereas Michael Anthony is much more central to the sound because of his distinctive high backing vocals. Then again, Alex's last name is Van Halen too, so Eddie probably wouldn't do that, unless he was in one of his cocaine freakouts.
Sammy Hagar seems like a perfectly nice guy, and intelligent/organized enough to build a decent tequila & Mexican food mini-empire before he sold it off. I have no doubt he'd be fun to have a few drinks with. But as a lead man, I found him a big step down from David Lee Roth. Better than Gary Charone, I guess.
OK, I've filled my quota of writing about Van Halen for the next decade.