I have owned all three (and still have TRON and LoTR), and for me it was:

TRON > LoTR > ST:TNG

Over the years I have found that I enjoy faster games that are not too deep as I am not a very good pin player and do not make it too far into the deep games. Also, I very much enjoyed the gameplay of ST over ST:TNG even though I can see why ST:TNG is such an amazing pin. In fact I prefer my IMVE to TRON, even though I love both and they are long-term keepers for me. It is not, then, just theme to me but also how much I enjoy playing the title that factors heavily into which pin I might keep or move. For example, if I my wife did not "forbid" me from selling LoTR I would have moved that instead of my TSPP as I found TSPP more fun to play than LoTR.

Yet, as always, play the pins if possible and decide which you prefer!

This is a good point. I often do not have time to focus on the DMD, but with LoTR I feel that the dots are really well done.