Seriously lifetime is not really the main concern of a TV nowadays.

I was once reseaching for TV back few weeks. In the end I got a LED LCD for myself, 90% for aesthetic reason.

LCD - good in a brighter environment, energy saving, and lesser problem on worrying burn-ins, mostly full HD above 40", better for HTPC (primary concern of mine)

Plasma - cheaper on bigger size, better blacks, require a dark surrouding, less issue on ghosting (I heard)

Tht's a short point I listed out, hope it helps