If you want to strictly compare voice/range, Cherone is actually the best "singer" of the 3.
I saw the one concert where all 3 graced the same stage. When Hagar and Roth toured together solo in 2002.
At the stop here in Mansfield MA, Hagar brought Cherone out to sing on a few songs. By far the best vocalist of the 3. Also was pretty good as a front man on the VHIII tour. Just wasn't gonna fly with the public, but Eddie seemed to be having more fun on that tour than any previous I had seen. And because Cherone could sing anything and would sing anything, the setlist included a lot of Roth era stuff they hadn't played since Dave left as Sammy basically would sing Jump, Panama and You Really Got Me, and that's it.
Michael Anthony joined Sammy to play bass that night so the show featured every member ever in Van Halen not named Van Halen.
Roth had put together a hell of a backing band that tour, had the guy who played guitar in The Atomic Punks, probably the preeminent VH tribute band, and the guy was good. Exact opposite of the previous time I saw Roth solo when he was at his nadir, played a small club, Avalon, introduced his guitar player as a friend from middle school on his first ever tour, you could tell. Band sucked and Roth was bad that night, this was in 1994.
But truly Roth was the only proper front man for Van Halen regardless of his vocal shortcomings. The last tour they did in 2015, he was definitely sub par, but conversely the now clean and sober Eddie was the best I'd ever seen. As Laz mentioned, Roth's musical abilities are greater than many realize, he wrote "Intruder" on his synthesizer when they need to fill some time on the Pretty Woman video. And as far as front men/show men are concerned, he's the standard bearer for hard rock acts.