I'd go for blus of the whole existing series, and New Avengers too.
The 50th Anniversary UK DVD set is the way to go. I thought I would hold out for blu ray, but I just don't see a US release ever happening.
The Persuaders! series was released by Network on blu ray in the UK, but its locked to Region B. Meaning you have to buy a mod blu ray player to play the discs.
I see the same thing happening with UK releases of The Saint, The Avengers and Return of The Saint (if they ever happen).
It's too bad the US cannot get at the very least the same new masters that were included on the UK set.
Oh the UK 50th anniversary set is packed with quite a few audio commentaries and many other features.
Anyway. I waited several years, but decided to go for the Anniversary DVD set. It's very well done. Highly Recommended.