Loved the part in tron where they (Flynn, Ram, and Tron) find the glowing water and they drink to get re-energized. I loved the entire look of that room.

In Tron: Legacy my favorite part was when Rinzler/Tron turns back to the good side, falls into the sea of simulation and at the very last second his colors revert back to blue.

I like the Lightcycle scene. It still looks good today. I grew up after TRON and learned about TRON through Legacy, but now that I've seen the original, the Legacy lightcycle scene seems like cheating. JUMPING over their CURVY trails? Reminds me of a console game... I thought Evolution was decent though, despite poor reviews. And Legacy was OK from a more modern perspective. But the original was better in my opinion.

I'm going to throw a bit of a curve-ball on this one and say that one of my favourite aspects of the film (but not the only one) is interestingly enough the SOUNDTRACK.

Let me explain. Has a child I grew up in the 80's, and have a lot of fond memories of that era, especially the entertainment (and that includes the MUSIC).
I particularly have a soft spot for all the soft synthesisor sounds that was becoming popular during the early years of the decade, and were pioneered by the likes of Gary Numan, Kraftwerk and Vangelis.

There were a few films in the early 80's that did incorporate these synthesisor sounds into the scores-films such has Flash Gordon and Bladerunner being to great examples. If you go onto Youtube and look up the filmscores for both Flash Gordon and Bladerunner and you see what I mean.

When I began rewatching the original film years ago I noticed that, given the time it was made, there was some of this synthesisor sounds in there too. On some scenes (like when they're being chased on Solar Sailer it's quite obvious, whereas in other scenes it's very subtle.
I've got the original motion picture soundtrack on CD and when you listen to it it becomes quiet apparent. 

If I had to pick a particular scene (and there are a lot off them) I think it would have to be the I/O Tower. From the moment we first see Dumont has the Tower Guardian to the moment Tron receives Alan's orders and does his "Create a new world" speech has always fascinated me watching the film.

You can hear the etheral music in the background, and what I love is that it is the part of the film that strongly emphasizes the SPIRITUAL/RELIGIOUS undertones that run throughout most of story.

It's clear from quite early on that Programs view the Users has some kind of divine beings that are responsible for creating all that they know about their world, and the I/O TOWER scene shows that idea beautifully.

Dumont (with his beard and tall 'hat') looks like some kind of monk, whereas the I/O Tower could be viewed by some Programs has some kind shrine or temple, with which they can 'connect' with their Users (or Gods).

Watching Tron converse with Alan (who appears has a beam of light and a disembodied voice) could for him be seen has some kind of religious/spiritual experience.

When they made Legacy that religous undertone was replaced with a far more political one (with Clu's overthrowing of Flynn's influence on the Grid the equivalent of a military coup, and the creation of his fascist police state).