this is an old one.and i will give the "check it out for yourself" answer first.
.....depending on record size and count, (and other factors). the only true test is to check statistics [TIME and IO] against each executed (or estimated) running of the queries..
now for my opinion.
there is no difference between the two.
I prefer the ansi joins sheerly from an portability aspect. everyone who is anyone is using them (even oracle has switched to ansi joins as per 9i).
just me however.
A GIS for "join style" returns a consensus on this matter "no real difference but your code will be portable".