I've only tried 3 RY4 juices.
Vapor Alley RY4
Cignot 100% VG RY4
EC Blends 50/50 RY4
Vapor Alley had RY4 in I believe it was 70/30 PG/VG mix and it was the best tasting RY4 I've tried. However upon checking I see the only offer it in an 80/20 Ratio and its now called VA Premium RY4 and costs more (they were like $4.xx a bottle and its now $7.99 for a bottle. The old RY4 they had seems to no longer exist, so yea I can't provide any review on their current stock of juice)
Cignot has a 100% VG RY4 frankly I didn't care for it it had a funky taste.
ECBlend offers an RY4 that I've heard a lot of people speak very highly of. Personally I didn't think it was as good as the RY4 that Vapor Alley no longer carries but I've heard a ton of good things about it from other reviews online I feel like the only person who didn't like it so I'd say give this one a go, plus ECBlend has some of the cheapest juice prices around, and you can customize any juice on the site with their amazing options.
--Fair Warning on EC Blends while their price and selection are the best I've seen their shipping is the slowest, this is because they mix all their juice fresh after an order is placed for it and do not keep a pre mixed stock, it usually takes them 3 business days to process my order and ship it out then another 3 business days for me to get it in the mail. But considering their amazing selection, insane customization features to dial your juice's mixture in, and super cheap shipping its a fair trade off. Also this means you may need to let your juices steep for a few days/weeks depending on the juice and bottle size since you're getting a freshly mixed bottle of juice each time from them. Use coupon code 10020 with them and save a bit of money if you try ECBlend