SPCR

They all have a similar design, which do I go for?

I'd go R3 or 550D. Simply because both can block all the extra ports via vent blockers from each company.

Price wise the R3 wins but build quality is a bit better on the 550D.

Im choosing between these also (and R4), my requirements are GPU cooling (single overclocked gaming card) , hard drive vibration and general sound leakage/panel dampening.

I currently have a Antec Solo/P150 which is as quiet as it gets with very thick panels and antec hard drive system, but it lacks a bit of cooling and videocard length.

Bear in mind fans will be 800rpm max (pref around 600rpm) and I will probably block any fan ports on the top of the case, so just a 120mm low rpm exhaust and a 500rpm intake.
If I need extra cooling I will swap the stock 1155 hsf for my Noctua NH-U12P which will drag air across the motherboard and ram and push slightly towards the exhaust. You can get away then with a weaker quieter front panel intake, I may not not need one at all.
My Solo with a 5850 videocard only has the single 800rpm exhaust + top mounted PSU. Nothing is voltage overclocked so it cools well enough surprisingly.

Ive heard the Corsair 550D hard drive cages can lead to vibration, can anyone recommend this case?

Edit: Ive ruled out the P280 as Ive used it and its unexceptional for silencing, just a standard modern case for sound leakage but with Antecs hard drive grommets.

The fractal R4 is probably the best Case atm for a "silent" pc/gaming rig.

The corsair front is so starved for air imo.

The P280 is the best, Corsair, I don't care for the finish on it. Fractal is decent but you should also look at the Bitfenix Ghost. It's new slient case that's very much like the P280, Factual Design R3,R4.

P280 is a good general case that cools a quite powerful system fairly quietly, but after building a low-mid range gaming system in it for family member I didnt think it was that great as a super quiet case compared to something with panel dampening like my old P150/Solo (or the P182), or maybe the Fractal r3/r4 (I havent used them though).

The P280 is a good case but in my opinion its not a successor to the Antec P180/P182 for a super quiet system that doesnt require big cooling

If anyone has found differently be good to know

P280 and R3/4 are far to big for my liking. I happen to live in a place where rents are topping out year after year, so small but quiet cases are more to my liking. Of course, that does rule out any 2way GPU systems.

YMMV.

You can't even compare the P280 and the R4 for a silent system.

I tested both Corsair 550D and R4 and P280.

Corsair 550D ( front is starved for air )
P280 ( 2 fans on top? and mesh zzz, cant really make a silent system with that imo! not that its that bad the case is awesome for a really high end system).
Bitfenix Ghost (to much mesh)

R4 (overal best for silent case if you ask me).