Great poppers are very much a personal opinion and those opinions will always be shaped by how successful they have been for an angler and also the angler's popping style. Some people like to pop with an upwards motion with the rod in the gimbal whilst others prefer the side sweeping motion. Some poppers work better with one action over another. For example, big Hammerheads actually don't make that big a splash with a sideways popping motion but they create a massive bubble trail which really attracts the fish. On the other hand, if you pop with an upwards motion, you will create more of a splash.
I agree with you on the S-Pop - I still believe the original is the best but I do know a few people who swear by the GT Mania. I personally much prefer the Cubera which I have a great deal of confidence in. It's a matter of personal choice.
I think Brandon is spot on - especially the first sentence. Having worked 130g GT Mania and 125g Cubera in conditions varying from flat calm to decent sized waves, I have had success with both poppers, using two basic techniques, over both shallow and deeper water. I doubt that my technique is up there with more experienced poppers but for what it is worth, I found the following -
In flat calm conditions, I found it relatively easy to work both poppers with either a fairly short and violent upward motion or a longer sideways sweeping motion. As Brandon says, the former created a pronounced voluble pop and the latter less pop but more bubble trail.
In a decent wave, I found it necessary to time the retrieve. An upward motion especially tended to skip the popper off the top of the wave. So I aimed to pull hard when the popper was on the backside of the wave i.e. when the popper was out of sight. A sideways sweep was more forgiving in these conditions but still worked better off the back of a wave.
Have not tried the Skipjack yet but am taking a few to the Seychelles early December so will see how they do.