It's a little early for a fair comparison of these games due to incomplete code on both. GNR code feels a bit further along than LZ at this point. I only played the pro LZ and the LE of GNR so that's also not a fair fight. So a few pros and cons of each so far imo:
Pros...beautiful playfield, cabinet, light show, theme integration, risk vs. reward aspect of rules, great video and song assets.
Cons...too multiball heavy (reducing the helper mode multiballs would help), bad plunger shot that dribbles to right slingshot, JJP flippers. Also, newer players have trouble knowing what to shoot for and why. JJP games have great lights, but when they are all on and changing colors, it's hard to tell someone "hit the lit shot", so it becomes a flail fest for this type of player.
Pros...fast action, snappy flippers, good flow, good pf layout.
Cons...rules need more love, pro playfield is sparse, theme integration isn't fully developed, feels similar to many other games (lack of uniqueness).
These two are very different games and it's going to be a matter of which game style you prefer as to which you'll like better. Collectors will lean more towards GNR and tournament players more towards LZ I would guess. Many people are a little of each (players and collectors/enthusiasts) so they should get both!