I voted "any", as diversity on the long run is the winner
The party vs one big creature is simple and leaves little to strategy, since each PC is just trying to using his best features. However it is good for those moments when you actually prefer something not too much tactic-intensive.
Party vs horde of cannot fodder is also nice because it sometimes make the characters feel powerful as they wade through the enemies defenses to reach the BBEG. The real drawback is that it could be very hard for the DM, so when it happens I often have to just skip the turn of a large part of the horde.
Party vs equal party has great strategic appeal, because each character generally has to "pick" his own target, only that the target which is weaker against your tricks usually has the tricks you are weakest against... so who do you take? Fighter vs fighter & wizard vs wizard or fighter vs wizard? Usually it's the most interesting combat situation, but with a serious drawback: if the opponent party is close to be on par with yours, death of some PCs is very likely (which just means that you cannot have a really matched party vs party combat every day), and if it is otherwise weaker it of course loses the appeal.
You can make the greatest use of this fights in campaigns with variants which allows for combat to end without real death more frequently.
The other 2 combats are much more rarer: one vs one (or "duel") only happens in very specific story circumstances, because letting one PC fight alone while the others do nothing is just unconvenient; the party+allies vs army (or "warfare") is very hard to run with core rules, and you definitely need some extra rules to make it work, and even then it is usually painful enough to make it happen only occasionally - not to mention that the whole D&D is focused on small-scale.