The 90s Gundam OVAS are all fantastic in that regard. 08th MS Team is my favorite out of them. The Patlabor movies also come to mind.https://www.invidio.us/watch?v=XHoCPtWaCtwhttps://www.invidio.us/watch?v=IsMTpSDAGxM
For a more controversial statement because >3DCG, I think Majestic Prince had the best mech fights of the past decade.
FYI We already have a mecha thread >>845