IM VE & Tron are the two of the 10 best pins of all time (IMO).
This is just my humble opinion and if I was starting a collection these would be on top of my list (as well as AcDc premium).
I play IM more often than any of my other pins, yes it's the newest but even factoring in when those pins were new IM hands down gets more plays.
Plus if you are looking for a theme both are great with sound and callouts (Jeff Bridges is the man).
Tron is also in the style of IM in that the rules are rather basic and easy to accomplish, probably Tron is a bit tougher to complete some of the modes but on the whole they play similar (quick) with the edge in code overall to Tron but the layout (IMO edge goes to IM since Tron basically has a lot more on the left side of the PF while IM is more symmetrical).
Tron has the edge in music and tone.
Callouts are about the same.
Gameplay, IM is more frenetic, Tron is more Zen.
Art/looks Tron has the slight edge.
Unique shots both are nice, with center shot on IM especially, and Tron has nice inner loops (like Quarra which I really like also Tron probably has more shots with 3 flippers.
Tron also has a real skill shot (much more than IM).
Seems like the modes in Tron are more interesting.