Depends on budget, but plasma gives much deeper blacks. LED looks better under shop lighting as it looks brighter and sharper, but watch a bluray at home and the blacks look grey and you lose definition between dark objects, often referred to as 'blocking'
Find your local richer sounds and ask for a demo of both in their demo room, watch a few mins of different media (DVD, tv, blurry etc...) and then make your mind up which you prefer.
Personally I still love my 3 year old Panasonic plasma, not a good looking tv compared to modern stuff, thick body and wide frame, but far more realistic picture.