I'm planning to buy a wide angle lens for a 550d to use it with a steadicam merlin.
The tamron lens is cheaper but not as fast as the tokina. But since I am in a tight budget I'm thinking to go with the tamron.
Does anyone have any experience with it especially in night conditions?
Thanks...

I can't comment on the Tamron by I have the Tokina and have to say that it is an awesome lens. Super sharp and get value for the performance.

Does anyone have any experience with it especially in night conditions?
Thanks...

I film with it regularly in 'nightclub' conditions, and wouldn't sacrifice the extra stop or two over the Tamron. And yes, blisteringly sharp and relatively distortion free.

Is it worth the 40% extra? If you intend to sell or earn money from your work, yes. Don't hesitate - get it. It's got me shots that would not have worked with the Tamron or my usual workhorse - the EX1 (even with a wide angle adaptor that costs the same as the Tamron).

Don't forget the benefits of DoF at 2.8 - it blew my mind when I realised I could get a blurry bgd and sharp action with such a wide angle lens. I get paid to make things like people writing on a white board look sexy, so the Tokina paid for its self that day.

Invest in good glass.

Invest in good glass.

I think you're right!
Good glass is an investment...
I think I'll go with the tokina because of the 2.8 stop..
Thanx