Dave, and it's not really close.
Sammy is a better singer, no doubt about it. But Dave has the personality and stage presence. One of the all time great front men.
I've gotta vote Dave but I think both were completely different very good bands. There is just something about the early years of VH that is just classic.
DLR songs had a bigger impact on my young life and will always remember where I was and what I was doing when each particular song comes on. But I probably enjoyed Sammys songs a little more. Hard to pick a winner cause they both impacted my music life positively.
I voted both - I'm a huge VH fan, and like all their music (even a few songs off VH III with Gary Cherone). Like @Nate, the DLR songs had a bigger impact on my young life, and still bring back a lot of memories of my youth. I saw them twice in concert with Dave - first one being the 1978 World Tour, when they were the opening band for Black Sabbath.
Dave was dynamic and had a great vocal range, but was a complete ass in live shows. He was always hammered, forgot the words to the songs, never sang them like they sounded on the album, wandered off and did monologues in the middle of songs - the show was all about him and his antics. Sammy was much better live, he was less of a showman and more of an actual musician, part of the group rather than trying to hog all the limelight like Dave did - if you wanted to hear VH do VH songs that actually sounded like VH songs, Sammy wins hands down, and it ain't even close. He also added another dimension to the band with his guitar playing, even though he can't hold a candle to Eddie guitar-wise.
In the studio/on albums, I liked both of them equally. There were a lot of great songs from both eras and they're both still heavily in my listening rotation. In live performances, I'd take Sammy every time.
Both.
I loved the original VH, even though I thought DLR was a bit of an egotistical ass. The music they put out was incredible though, most of their really iconic tunes were from that era.
I was a SH fan all the way back to Montrose, and saw him live many times before he joined VH. When I heard he had joined VH I thought it was great, such a good voice, and a second guitar. Definitely a different band, but still great, just in a different way.
Sammy Hagar is a much better lead singer than Diamond Dave. Dave got the better songs, but that is just a product of bands using most of their creative juices in the early years.