Between the two... I have no preference for brand either way, so I would have to go by the Aesthetics and from what I can tell from pictures I got from Element Vape. i'll link the site so you can see the pictures and info that I'm looking at.
The Voopoo drag, looks like it's a "classic" box mod design. It reminds me a lot of the Sigeli 100 I have. It will be thinner with fairly squared off edges. Looks like Stickers on the doors, which actually help from scratches, in the future. However, there still will be no protection from the edges, which will get dinged over time. Because it's thinner, it won't sit as well on a table, and the heavier the tank you put on it, the more prone to accidental knockover it will be. The 510 looks solid, and is slightly risen from the box, leaving room so the atomizer doesn't scratch the top of the mod when screwing it down.
The Vapresso Revenger looks more Aesthetically pleasing to me. It has a larger screen, and displays the power level of the individual batteries which is useful for determining if you need to swap the batteries out. It is a larger mod, and will be pretty stable setting it down on the table. The buttons on the front of one side means it won't be advisable for left handers, since using your left hand will cover the display, and possibly push some accidental buttons. The chipset looks newer, and might offer a more stable power. This mod, however, looks like the sides might be more scratch prone as well as the 510 on top being flush. I believe screwing the atomizer down will scratch the top of the box.
Overall, I would probably go for the Revenger. I wold find some sort of go-between for the 510 (I do that anyways now) like a Kepler heat sink. Neither will be pocket friendly, however I think the Drag might be more portable in the long run. I think the Revenger is just a newer design.