Bored and waiting for a spawn...so blah blah blah:
That site rates uncommon ACs "equal" to regular ACs. Its a nice stats list, but not as material to what you want ingame. It ends up giving obtru a higher total stat than flowers, but obtru has low melee (ow), where flowers has low poison (who cares).
PvM is pretty simple, and nearly universal with missions and most camps. Some camps will favor one of the big 3 over the other 2.
-Most common: Projectile
-Close second: Melee (tend to hit harder too, I would rate it equal to proj due to this, less likely to be minimum dmg)
-Strong third: Chemical
-Weak Fourth: Energy (mainly at lower levels with bots)
-Everything else: 50 times rarer and only on bosses, a few dungeon mobs, some rare outdoor mobs and occasionally MA mobs. Nanos have such high minimum damage it hardly matters what they hit with.
Anything that is low in the first 3 is a substandard choice for PvM if you have a choice.
PvP is a little different, but half damage tends to favor weapons can hit hard. Everything else ends up minimum or a crit. Crits don't ignore AC, but are so big (or capped) that AC can't help as much.
I'm no expert at PvP by far, but you can look a the weapons around and get a feel. Energy, melee and proj are very common, and Chem (MCS, MA) Fire (Adv, MA) and recently Rad (Sold) show up frequently. Cold and Poison are rare and don't do much damage. Nanos again have such high minimums it won't matter as much.
PvP makes things like Decaniums + RRFE more effective than most armors, esp for non healers. (nearly 1000 extra life + half damage + 30% reduced is like getting 2500 life in pvm, even better if you have HoTs and heals) It also has its lower ACs in the least common areas.
Dragon can be OE'd to hell and back if you're not a MA user. (personally I hope to drain first) Only the body gets better ACs, the rest is less per AC than some type of regular ql200 armor. Body, legs and circlet give good bonuses, the rest are almost pointless to everyone but some MAs. Looks nice though :D