Fastest way to kill heavily armored guards in a group?

I actually just finished this game yesterday, here's the ways I dealt with Brutes:

• If you aren't actually in a conflict (the guards are just standing around or walking and you want to fight them for whatever reason), try to start with an assassination of at least one Brute in the group. You can usually get above them and do an air assassination, even better once you get the double hidden blade and can take out two guards immediately.
• If you're already fighting a lot of enemies, Smoke Bombs are one of the best strategies, throw one down and then try to assassinate as many Brutes as possible while all the enemies are disabled. Repeat as necessary.
• If there's not a lot of enemies hitting you at once (which can make it difficult), disarming a Brute works really well. Switch to unarmed, and then it's the same command as a counter-kill (RT+X on 360) when they take a swing at you. This will take their weapon and you'll be able to one-shot them with it by attacking immediately after the disarm. Watch out for "Smash" attacks though, which you can see them charging up before they swing. You can't disarm during these, you'll get knocked down if you try. Use the dodge move to avoid them instead.
• If it's a conflict that you get to initiate, it can help a lot to hire Mercenaries to fight with you. They'll keep some of the guards occupied (hopefully the Brutes), and you can then backstab them for one-shot kills.

For the heavy's I've done it a couple of ways, the easiest (only IF you know you're going to be attacking a heavy) is to use the hidden blade and kill then first.

During a fight use smoke bombs, throw one down, they all start coughing, kill heavy's with hidden blade. Or you can get out of combat and start running around, using strafing I think, try to get up close to the heavy's and use hidden blade.

It's been a while since I played this game... and don't have access to my copy (it's on loan to a friend half an ocean away), but if I recall the correct guards you are looking to kill, I believe the only way I handled them was getting really good at counter attacks / disarms. Taking away their weapons and one-hitting them with it.