I use World-of-ai its freeware and good but if i was getting payware def ultimate traffic

I have no experience with just traffic but after nipping over to the just flight website it certainly seems to be lacking realism 

I have the old UT from justflight in a box, (I can't remember how old it is) and it seemed to do the job, some parts of the world are severely lacking in traffic, mainly Russia and Africa, but I found the Traffic board function good.

(Judging from the screen shots) UT has better models and textures (although you can always download separate models and replace the old ones) and I don't think that its very realistic to be adding the A380 into traffic just yet.

I suppose in the end its up to you, personally I would go with UT but only because of my experience with it. It would probably have good better by now as the version I had I used in FS2002 aswell.