Which is best and worth buying!
Thunder tiger E Mta
Or
Traxxas Slash 4x4

Both electric

Depends on what you want.

The slash is a more realistic car but can't handle the terrain that the E MTA can. The E-MTA is a little harder to work on compared to the slash.

Traxxas  E Revo brushless 56087

             Or

Traxxas slash 4x4 ultimate 6807L

Which is the best?

Is traxxas E REVO BRUSHLESS good for proper off roading than slash 4x4 ultimate

Hi Daanish, E Revo is kind of both on road and off-road, but off road needs tyre change if u want regular running on offload and also depends what kind of off-road surface it is, kindly muddy place like we see on rough tracks, compare to this slash ultimate 4x4 you can is
more of off-road car.

If you looking for proper off roading then try at summit or stampede.

Njoy...

You should consider the MT4-G3 which is much more reliable compared to the E-MTA.
The MT4-G3 also handles and corners way better on a track .

E-MTA design has already been changed now to E-MTA2 ,where as the MT4-G3 desgin is unchanged its design origin dates back to 2006 from the undestrictable ST-1 truggy ,it also has lots of parts interchangeable with Team Associated RC-8/T(both companies owned by thunder tiger).

MT4-G3 is the basher approved and is bigsquidrc official demo truck (previously it was held by HPI Savage).

If you want a no non-sense easy to drive and low maintenance Electric monster truck the MT4G3 is the way to go. It may not have the brand brag value and may not look as good and comes a little cheaply finished as an over all RC product/brand  it has the right mix/balance of metal and plastic parts because a bent/broken plastic part can be fixed/replaced easier than the same in aluminium and costs way less. That said even the stock tires are really good and offer good traction and less wear for a hobby grade product. I have upgraded the 3 diffs to silicone oil and the thing holds crazy wheelies and does stoppies too!
Like others have suggested it depends on your use at the end of the day. Also watch bigsquid rc review on the MT4g3.

Slash 4x4 without a doubt !

Mta4 G3 which is modified and lifted st1 truggy . Beats everything for Bashing and has decent track behaviour 'out of the box'.Trx slash is pure crap compared to a truggy. Slash is ok in stock form but not close to mta4g3 in performance, price, durability. Slash needs a lot of mods to work well. I dont know anyonelse with a stock slash that is not modded. It needs it. Slash feels like a more like a toy when u drive the two.