Given the options of using Zephyr and Xtreme in competitive play, I'd have to say Accel is still my go-to attack driver. I'm not a fan of X in particular mainly because of the small window it leaves you to land satisfying, burst-inducing hits. Tornado stalling tends to mean certain death for X combos because of how quickly it loses spin velocity. Additionally, even when shot by experienced users, the fact that the part performance depends so critically on the state of wear on the part (too unwieldy for most when not broken in, but also prone to eroding away) combined with its aforementioned poor stamina, is a dealbreaker for me.
In addition to being easier to control, Accel's respectable attack speed and movement patterns combined with its decent stamina make it a winning part. When launched properly, it is still possible to achieve tight flower-esque movement patterns that will deliver some satisfying hits to an opponent early in the match. Should this pattern not take, however, and a tornado stall occur, my Accel combo will lose spin at a much slower rate than an Xtreme combo, meaning that when it's done mucking about on the outer rim of the stadium, I've still got those crucial RPMs that allow it to deliver heavy hits to the opponent, and the window for delivering such hits is much, much larger than it would be with wider attack drivers. It's also not uncommon for me to have come out of a tornado stall with enough power left to both destabilize the opponent enough to make them lose spin by hitting the stadium floor, and then winning by outspin.
I've found Zephyr to also share most of these benefits, but much like HF in MFB, I've seen that Zephyr is too fragile a tip, with a higher risk of denting and deforming from regular use. This is not a worry with Accel, and provided I keep it away from concrete surfaces and hungry children, it should remain a much visited piece in my war chest for a long, long time.