Yeah, I'd go for the Prog 582 Fabry cover meself - it's the least 'generic fantasy' of the lot, despite being the simplest.
However, that said, I think the Collins/Farmer image is pretty striking, and we've already had a pretty shonky piece of early Fabry on Volume 2, and will probably have Bisley on any Horned God volumes and Power on the Time Travel volumes that continue this edition. So having a strong image by one of the other Slaine artists of the period on Volume 3 makes sense.
What i don't understand, and what's stopping me buying beyond Volume 1 (Best. Cover. EVER), is why they chose a weak Fabry for Time Killer. To my mind McMahon's best ever work is in Volume 1, and the Time Monster Cover is some of his very best work, so it's a no-brainer. Then Volume 2 belongs to Bellardinelli - Dragonheist is his finest moment on the series, and one of my favourite sequences from all his work. Fabry has some great work in Volume 2, but he really shines in Volume 3, with Slaine the King and Warrior Niamh. So give him the cover of Vol 3. Reissue Volume 2 with a Belardinelli cover, and then 3 with a Fabry cover, and you'd have two new sales.