The Mountech front is about as good as front derailleurs get. The rear... not so much- depending on the version it was either a time bomb or clunky and clumsy. Either way- it was too complex for what it needed to do. But the front was fantastic- it had a huge range and it was reasonably heavy duty all the while it's still lighter than many "racing" derailleurs these days.

I like to have things in a 'matchy-matchy' sort of way- even if that 'match' is in my head, and if it doesn't match or meet my aesthetic expectations it'll bug the living daylights out of me. So I guess it depends on what you have for your rear derailleur. Any of the old ATB derailleurs should be good on a 26-38-50 triple- I don't have any experience going above 50- I don't know about the cage arc.

If you're rolling with pre 1986-ish derailleurs- I'd go Mountech.

If you've upgraded the rear derailleur to an @5000... I'd want to get something fancier on there. If you like Suntour- XC Pro and XC Comp are both dominant and would look cool as all get-out on there. If you like Shimano- I'd recommend MT-60 Deore, MT-62 Deore II, the aforementioned M650 Deore DX, and of course, M735 Deore XT.

The Shimano stuff is cool because if you choose to change to indexing- your choices are much more wide open- all the old ATB SIS stuff uses the same pull ratio and Shimano 6,7 and 8 speed stuff is pretty ubiquitous. MT-60 is cool because it's all silver- has a good classic look to it. MT-62 and M650 are silver with the black decals... if the decals aren't faded or coming off- it looks sharp. Deore XT from M730 to M735 is among the best of its day (I think just below Suntour's XC Pro), and it looks really nice- but the M735 is the nicest.

Of course, this is just me being a dork and spending someone else's money.