Good question...but I do not have definite answer for that.
I'm having a bit of trouble with public vs. beta.
Some public projects were never running at >90% availability of server or work (LHC, Protein)
Some public projects have regular outages (SETI, Protein)
Some public project lack feedback from core team and/or admins (Protein, LHC)
Some beta project do have work and are running on more regular basis (Malaria came to my mind)
Where to put SZTAKI which gone mad recently?
In those aspects, some beta projects are superior to public ones (perhaps Malaria)
For sure, there are stable and reliable project - with Einstein on the first place and in long-term; with CPDN right after.
I got the impression that stability of scientific application makes project beta or public but this single attribute doesn't make me give it a gold mark.
There was/is a thread about BOINC project's quality, which I can't find early in the morning...