There are Miniart kits without the interior so you would only pay for the outside parts.
I think the Miniart kits have more parts than Takom T-55's.

If you are happy with the rest of the Tamiya kit there is the option of buying just the tracks.

If you are still interested to build another T-54/55, you can go with either of them. Miniart also has the w/o interior series, as Mr. Nilsson said. The price are comparable.

Then, it is down to which version you want.

T-55:
Miniart one doesn't have the roof MG, it might affect some people.
Takom counterpart is the Type 69, this one has roof MG.

T-55A:
Miniart has several T-55A, aside from the T-55A mod 1981 (also the only Miniart T-55 with the roof MG), the other (mod 1963 and 1965) are pretty the same externally. Both of them are just the bare base model.
Takom has a single base model of T-55A, then they have several modernized T-55A, like the T-55AM, T-55AMV, T-55AM2A, with different exterior feature like ERA, boxes and optional exterior load. They all have roof MG.

T-54:
Miniart has some prototype and early T-54, such as the T-54-1 and the T-54-2, these T-54 are all different externally, specifically the turret. The T-54-3, T-54A and T-54B are about the same externally.
Takom's counterparts for the T-54-3, T-54A and T-54B are the Type 59 and the T-55B.

I mention the roof MG several times because the T-55/T-55A in the Soviet service don't have it, but the majority of the exported T-55/T-55A do have the anti-aircraft MG.

I recommend to get the Takom ones, because they have more decal options and possible build than Miniart. Still, Miniart has versions that Takom currently doesn't have.

Edit: There are some problem with the T-55 wheels (http://armorama.com/forums/271132) not sure if it apply to all of Takom kits.

I have the Tamiya T-55A, Miniart T-54 and Takom Type 59 and T-55AMV. Takom's molding is beautiful, then again so is Miniart's now. Price wise the Miniart I got was around £10 cheaper at the time, although I think Takom's have come down a bit. Biggest let down from Takom is still the two piece barrels.....you won't go wrong choosing either, just depends on vehicle and price. But for your Tamiya could still pick up a barrel, etch and tracks for less than either of the other two.

In another recent thread you could find your way.
But it all depends of the 54/55 version you want to depict.
Tamiya T55A has several dimensionnal issues and version errors. I have 4 in stock and will build one as T54 ( the wheels and turret are corrects for) and one as Cz build T55A (need lot of works and after-markets parts).
The Takom kits are all accurates , well detailled but have some little problems and the T55A can be build only as late T55A (late tracks) from the box.
The Miniart kits are THE choice for russian build T54/55. Accuracy, detailling,tracks are excellents. The only low i see is the lack of DSHK machine gun that is nearly always see on exported version. Their Late T55A have it but the late tracks are rare on exported T55A (excepting the tanks given to north alliance in Afghanistan.

So for T54 A or B > Miniart
for Early T55 (russian build) > Miniart
for T55A > Takom for Cz build , Takom or Miniart for russian build
for late T55A > Takom for Cz and russian build or Miniart for russian.

for T55AM/AMV > Takom

Due to the contours of the barrel, the two-part is still quite beautiful. I have built two of them and there are no seems present. No putty. No ca glue. A simple swipe, with a #11 blade along the bottom and it is good to go.

Chinese Type 69 is quite different from T-55, despite Iraquis called it 'T-55 Chinese model".