I have recently purchased both Meffert's Master Cube and ODDZON's new Rubik's Revenge. While I preferred Meffert's efforts for general solving for several reasons, ODDZON's version performed far better when it came to speed-cubing.

Meffert's 4x4x4 Master Cube is unquestionably very solid and well-made, and it feels heavy and solid in my hands. It turns smoothly and does not pop pieces easily. The colored tiles (instead of stickers) are great, although they unfortunately don't conform to the standard color scheme. I just popped them off with a knife and glued them back on my favorite way. (Incidentally, you will find a very fun problem to solve if you try to minimize the number of tiles you need to switch in order to correct the color scheme).

ODDZON's Rubik's Revenge, on the other hand, is a bit more likely to pop pieces, and feels slightly more fragile. The version released during the winter of 2000 still uses the horrible and infamous ODDZON stickers that wear off quickly, so I would prefer the Meffert's simply for the tiles.

When it comes to speed-solving, however, I found the ODDZON cube to function better than Meffert's. The main difference is that the ODDZON cube tolerates more misalignment than Meffert's when you try to turn a face or slice. This means that when trying to speed-solve with Meffert's version, you will get "stuffed" more often, which also leads more quickly to wrist injuries (if you are speed-solving often). With ODDZON's I often get times around 1:40, while it's hard for me to break 2:00 with the Master Cube. I guess the difference is subtle unless you are really trying to solve it fast, so I'd only recommend the ODDZON version if you're trying to break the world record!