anything of 'normal' gravity that is not meant to be consumed very fresh (milds, bitters, IPA's etc) about 1-3 weeks after packageing I find them to be in the sweetspot (although I have really enjoyed an ordinary bitter that was just a day or two old).
Anything of 'normal' gravity that is meant to be consumed very fresh (weizens, wits etc) as soon as you can, particularly with styles that include a lot of suspended yeast in the flavour profile (hefe, wit). after just a couple weeks these, in my experience, tend to start losing something. if bottle conditioned some of this can be got back by inverting the bottle prior to pouring or swirling and dumping the last of the beer into the glass after pouring.
Anything with high gravity and lots of hop aroma/flavour (IPAs, IIPAs, American barleywines) give them a few weeks to mellow but not too long because those hops start to fade quickly.
Belgian strong ales (doubles, BDS, Tripple etc.) opinions vary. I like them fresher ( a few weeks to a couple months) doubles tend to age a little better than triples, BDS slightly better still.
high gravity malt driven beers (wee heavy, english BW, dopplebock etc.) some of these age really well for years (bw for instance) others I think start to lose it after a year or so (dopplebock in my limited experience). I don't really know how a wee heavy would go though.