my number one choice is wisco,as they are a work of art and a joy forever

I believe that Wiseco are forged rather than cast , which means they need larger clearances to allow for greater expansion, and hence have a reputation for being noisy (piston slap) when cold.

Dunno really.

Can you still get Hepolite? I used them in my 250C back in 1977 against the advice of my local dealer and he was right, but they were cheaper then which was important to me. I had 3 seizures and 6 holed pistons in 13,000 miles over a year on both Yamaha and Hepolite, so probably my riding style as much as anything.
Piston metallurgy has moved on a bit since those days I'm sure, but I have no experience on Mitaka or Wiseco.

Dykes rings are technically superior due to the way they seal, but I think only available on OEM new old stock now, and pricey.

Peter

I believe Mitaka and ProX are the same piston sold under different brands.
I also remember reading somewhere that both are actually made by ART, who made the original OEM RD pistons.

Easy:

1st Yamaha aircooled pistons, always if possible!
2nd Hepolite RD aircooled pistons, superb quality but harder to get than yamaha
3rd Wiseco RD aircooled
4th?
5th?
6th?
206th Any version of an LC/YPVS piston in an aircooled, its not the make... Mitaka, Prox etc its the design, they are not good in an aircooled.

Dyke ringed pistons from A and B models are better than the later keystone, they only dropped them because they were more expensive to manufacture.

You can still get standard pistons from Yamaha, but you will get them much cheaper from ebay.com (US site)

Again the rings are available from Yamaha, but cheaper from ebay.com Rd 400 pistons would be good too, the spec says early 400's were dyke, but not seen one with them. Unless you get 400 pistons from Yamaha, it will be easier to get 350 pistons.

Burning holes in your pistons wasn't a hepolite problem, it was your timing and/or mixture.

Re wossner, if they are made for air cooled, ???

I run ProX pistons designed for the Banshee engine. Nice, and when I got them in the mail from Scott Clough they were marked, "left" and "right". Cool, huh? 4.8K miles of trouble-free operation. Be aware that the rings must be installed properly, i.e., in the correct lands. The "fat" or upper ring if installed in the lower land will become a real PITA to remove. Of course, I've always followed instructions and never got ahead of things so it never happened to me. Uh, uh...not Dave.