Assassin is by far the best and most useful perk in Tier 2. Hardline is a great perk too if you use Specialist or if you abuse low level kill streaks.
Other than that, Quick Draw is worth consideration. You'll ADS faster than anyone else so if you use an Assault Rifle or Sniper (LMG aim time benefits too, just not as much) you'll have a very good gun VS gun perk.
I guess it depends on your play style/weapon. If you use an SMG,Quick Draw it's kind of pointless because SMGs have pretty good Aim time anyway and probably benefit more from Steady Aim than Quick Draw because of the close quarter-hip fire based use of those weapons.
I'd say quickdraw is a very good tier 2 perk. Definitely better than blast shield. Best perk? no probably not. But nothing really is cuz it depends on your setup and play style. The pro effect of it is also quite nice. I have a few niche classes that rely on quick draw and it's pro effect more than any other perk. So for me personally, including it's pro effect, it's probably my favorite/most useful tier 2 perk.
I'd say quickdraw, assassin, and hardline are the best tier perks IMO. Each one of them can be very useful depending on how you build your class and play. Overkill and blast shield, on the other hand, are just not as good as the others no matter how you play in my opinion. But, meh, take it or leave it.
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Depends on the game mode, how you're going to play it, and what class you are going to use.
E.g.: If you're playing Team Defender and going to try and capture the flag as often as possible, then Blast Shield is usually the best choice - plenty of explosives and tacticals will be heading your way (Assassin is a waste if you are going for the flag, but is okay if you are going to support the flag carrier).
If you're using the Riot Shield or an LMG, then Quickdraw Pro is excellent for throwing 'nades etc, whilst keeping your shield or gun up as much as possible. Quickdraw on LMG's can also give you the advantage when surprised.