Honestly, I wasn't impressed by the first round of speed paints because they had a tendency to smear and reactivate. This second round though, I'm very happy with. The 2.0 formula completely fixed the reactivation and slow drying issue, but ad a result, the paint dries extremely fast. For 15mm, since your using much less paint, this does mean that you get little working time and have to be generous with your amount of paint, but very careful in application (so pooling goes where you want it to go).
Compared to contrast paints, which have been my go-to, its hard to pick one over the other. I really like the consistency of the AP 2.0 paints. They flow well, and more importantly, all the paints I've tried flow the same as one another. The paints also dry more consistently, and streak much less. Citadel contrast paints, however, probably have better, well, contrast, and some colors, like skeleton hode, create much more unique color shifts from recesses to highlights; AP2.0 pallid bone or bony matter, for instance, feel more translucent and the colour shift more one-tone.
In general AP2.0 is more translucent though, and it takes multiple coats mucn better. As a result, their paints also doesn't separate nearly as bad as Citadel contrast paints, which have a habit of completely separating in only a few days of being unused.
Altogether, I prefer some handful of colors from Citadel, and I prefer a lot of usability of AP2.0, not to mention the lower cost and color selection. If someone told me to pick only one to suggest to a newcomer, I'd probably recommend the AP2.0 mega or complete set, but my real recommendation is to experiment with one or two of the AP2.0 and see if your painting style fits the worktime and scale limitations, and if you're a more advanced painter, you'd likely want to use Citadel contrast and more "normal" paints because of how limiting AP2.0 can be, even if the results out of the box are very, very good.