Practically any clan mixes well with Skeelz but especially the clans with strong combat bonuses (Uppers, Montana, Bangers, Ulu Watu, Vortex) in a 5+3 preset. Your Skeelz characters ignore SOB and also function at almost full capacity when their bonus isn't active.
Mono skeelz is competitive but you won't get too many easy wins. Mono Skeelz has arguably the most consistent draws of any preset as their low * characters are fantastic. A 10* Skeelz hand can compete with a typical 14* or 15* hand.
Montana/Skeelz is a great combination. Pack your deck with a couple of heavy hitters -- Greem, Logan, Michael, Jay, and Donnie are good candidates. Then add the standard Montana walls/Spiaghi. Watch your opponent squirm.