I’ve been using the ATR mastering tape for last few years. It sounds nice no drop outs handles what I give it, pleasing to the ears has a decent musical quality compression.
Before that I used 456 it’s a really good tape for that machine has a soft tape compression. Buttery creamy kind of sound.
I used 3m 996 for years it was my go to favorite tape I never had any dropouts or any other issues with it. Very happy with it I don’t use it anymore but if you can find it, long in the tooth but you might like it.
I tried GP9 It was very clean pristine crisp sounding tape. No issues with it at all I just kinda liked the 996 better.
Right now the ATR is easy enough for me to get, it’s brand new I don’t have to worry about condition it’s always brand new. Some of the prices for used tape makes it easy to buy new.