Early on your first set of armor will be probably be either Annihilator or Mercenary (35/39). Both sets are fairly comparable, however Annihilator has a few more stat points and the chest bonus of 60 HP every 4 sec. helps add to overall survivability. It is also easier to acquire via RvR.
The next set to get is Beastlord (40/33). It has a bit less in the way of armor but the resists are nice to have and the cloak/gem/pocket item are good to wear (+55 weapon skill for 3 piece bonus) even if you consider the armor items sub-par.
The next level of armor after this is the Redeye/Sentinel/Conqueror/Dominator (40/45). Personally at this level I grabbed Conqueror and Dominator, as Redeye required a solid group as well as more time and Sentinel wasn't released at that point. Things get tricky at this point tho, as the stats start to be more defined along tank/dps lines. At first I wore 3/3 of each set trying to maximize my wounds but in the end found that the Conqueror 5 piece bonus (on being hit 10% chance to gain 100 wounds for 20 sec.) is just too powerful to go without.
Current endgame armor is Vanquisher/Oppressor/Invader/Bloodlord, and again I initially went for the RvR/Scenario sets. I now also have 6 of 7 of Invader and mix and match all three sets depending on if I am going for more dps or more survivability. The best general purpose mix I've found tho is 3/3 Vanquisher/Oppressor. The extra wounds seem to trump any of the later bonuses you get in the sets.
My general experience with the various sets is as follows -
Full Vanquisher is good for Keep and Fort sieges but your dps is just too low when solo. It also works well when in a group due to the six piece bonus (on being hit:10% chance for -3% group damage for 10 sec.) but having all that + block percentage is a bit of a waste when going 2H.
Full Oppressor is just too squishy even with all toughness talismans, the only build I've gotten to work alright with it is 4/2 Oppressor/Invader and the four piece Oppressor bonus (on hit: 10% chance for +1% damage for 15 sec. stacks 5 times) is a bit underwhelming.
I just recently got my sixth piece of Invader so I haven't done much testing with it, But it looks to me to be better used with sword and board. It is nice to mix in 3/3 with the other sets as it surprisingly adds to overall dps. Once I have the gem for this set I think it will be nice to use it mixed 4/3 for the extra toughness.
I don't have any Bloodlord yet, however
looking at the set in the preview thread for it it seems that you would be very squishy wearing it as only one piece has any toughness. The sets saving grace may be the 7 piece bonus, only time will tell tho.
Edit: For the record I'm currently wearing 3/3/3/2 set wise for armor and jewelry -
Oppressor helm, shoulders, and belt.
Vanquisher carapace gauntlets, and boots.
Beastlord Cape, Gem, and pocket item.
Genesis Warrior fragment and remnant.