I’m wondering whether I should ask Santa to bring me the Oxford Classical Dictionary. However, the BMCR doesn’t exactly praise the 4th edition and some amazon.co.uk reviewers actually seem to prefer (or almost) older editions. Any opinions?
The Cambridge Green & Yellow on the 5th book of Herodotus I’m currently reading makes constant reference to the OCD – not very surprising, since both are edited by Simon Hornblower.
Please not Santa! That’s a dreadful word. Father Christmas is much more stylish. 
I tend to use the RE where needed, but that is old. Then there is Der kleine Pauly, but even that is 50 years old. Der neue Pauly is up-to-date and can easily be obtained online via institution. But I think you may be right, perhaps more concise, one-volume reference work would be handy. I haven’t really used OCD much, but here’s Duncan Campbell’s review on BMCR, possibly of guidance.
It’d be nice to here people’s experiences of OCD.
I have the second edition, which I like. I bought it because it was far cheaper than 3rd or 4th editions, and because I’m skeptical at what limited revisions of reference works like this ever really accomplish.
The third edition is significantly revised. I haven’t seen the fourth edition.
My own feeling is that with OUP older is nearly always better. That’s certainly true of the physical properties of their books. But I also feel that their revisions are hardly ever in a good direction. The scholarship may be more up to date but it seems to me that these days scholars look at pre-20th century periods as observers from an alien civilization (one I don’t belong to), with a distancing modern perspective, full of modern assumptions, which I don’t share, don’t like, and don’t find helpful.