I've played those for a while.
I've completed a lot of them, and at least tried them all.
I'll give you my thoughts on them all to save you some time.
Super Hostile 01 Sea of Flame II Difficulty: Average, Open-World
--This one is very well constructed, and all dungeons are unique. Some of the last dungeons are easier than the first, however. This one takes some more setup for SMP, as the default spawn places most players in lava. In order to get this running, the spawn point must be set with NBTEdit.
Super Hostile 02 The Endless Deep Difficulty: Easy, Linear
--Sucks balls, don't even load it up for a second. Also lags to shit on multi
Super Hostile 03 Infernal Sky II Difficulty: Easy, Linear-Branching
--Arguably the best of the series. Fun, imaginative, and very, very adventurous, this is the best, especially for SMP.
Super Hostile 04 The Kaizo Caverns Difficulty: Hard, Linear-Branching
--It has good ideas but pulls off too much bullshit. Not bullshit in the fact that there are traps everywhere (that's great), bullshit in how the map hides wool in places.
Super Hostile 05 The Black Desert Difficulty: Hard, Open-World
--Have not played this one very much, but it appears to be bland... sand might cause some lag, not sure really
what to say about this one. Never got a wool on it (and didn't really try)
Super Hostile 06 Canopy Carnage Difficulty: Average, Open-World
--Oh man this one. Trees fucking everywhere. If your computer sucks, you HAVE to turn on Fast detail. This one is quite the monster of detail, and seems like it would last longest in SMP. Problem is the same in Kaizo, where it hides wool in some of the most ridiculous places. Might be okay if people can handle it.
Super Hostile 07 Legendary Difficulty: ROMhack Hard, Linear-Branching
-- This one is a classic. And detailed. And assholish to the core. This one has to be the most detailed, well thought out. I'm considering calling this one the best if it wasn't for two of the wool pieces in the map... This one should definitely be considered.
Super Hostile 08 Nightmare Realm Difficulty: ROMhack Hard, Open-World
-- This has quite a few problems for SMP
1. SMP spawns are totally broken, so every new client has to have their data edited.
2. Permanent loss is extremely easy (see Red Wool
3. Cobblestone is a very limited resource
This one is barely acceptable for 2 people.
Super Hostile 09 Sunburn Islands Difficulty: Easy, Open-World
-- This one is short and kinda nice. Kinda, it uh, sometimes suffers from bad design and isn't that entertaining.
Now, what I haven't considered is the race for wool. If everybody can complete Infernal Sky either with a friend or on their own, we can play the competitive race maps.
EDIT: Also, all the maps I listed above besides 08 require 1.7.3 to be played correctly. If you guys don't have a backup jar of that version, I guess I could provide it (as long as you already own minecraft).
Race for wool 1 uses 1.7.3, but Race for wool 2 uses 1.8.1 .