Basically there is no difference on the ESXi side, it more for what the Guest OS sees.
for exsample SQL is licenced per Physcal Socket(for 2008 anyway) so for a virtual you would select 1 socket and as many cores as you need.
There is no rule of thumb for this as it doesn't make a shred of difference to the Hypervisor what configuration you select, but I usually go 1 socket 4 cores. and when it comes down to licencing thats when i would deviate as needed
Cheers