Best one?

All personal opinion. I've only tried the flip HOLE white and the flip HOLE black. The black feels tighter, has a slightly stiffer material, and has a more "aggressive" texture with a lot of "sharp" edges (as opposed to gentle round edges in the white model).

For me, personally, the flip hole white is total heaven. I can go for hours with it if I had the time (I'm multi-orgasmic).

Since I'm not into the "death grip", I didn't really like the black one at first. However, after a little more experimentation, I found that using a really light lube instead of one of the thicker ones worked really well with the black one.

My understanding is that Tenga is making the white models less "stimulating" than the black ones, so there should be a similar difference between the black and white flip AIR models.

Also, Tenga makes "lite" versions of these products. I've read a lot of complaints about them being too small for average guys. There is a size chart floating around the forum that gives a reasonable description of the size ranges for each of the Tenga products.

Personally I own two, the Flip Air White and the Flip Hole Black (the latter of which I'll be reviewing soonish.) The difference between them is pretty vast, so it kind of depends on your personal preference. The black models tend to have defined textures that are more noticeable as opposed to the softer white ones with their toned down patterns. The Hole isn't as tight, and expands readily while giving you the ability to put pressure where you like it, whereas the Air it very tight and only allows you to adjust the pressure overall (between tight and "sweet Lord my penis is in a silicone vice.")
Honestly, try to visit your local upscale sex shop. See if they have any models on display so you can compare them yourself in person. If that's out of the question though... hmm, which to chooooooose... well, the Hole is probably the best multipurpose toy even if it isn't as pretty or discreet as its newer brethren.