Budapest! I'd say Budapest first, Prague second, the rest doesnt compete.
OK, I havent actually been to any of the rest. But I'm sure they dont compete anyway
Depends though. If you're really just going for the one day, Prague might be better. It gives itself readily, so to say - its an instant hit. You walk through the old town, across the Charles Bridge, up the Castle Hill - you know, the first things you'd do as a tourist - and it just serves its charm up to you in eager helpings.
Budapest's sights are further apart from each other, and apart from the obvious (eg Castle Hill), the city's charms give themselves a little less readily. Example: the river. The Danube is broad and mighty, but in most places there's a tramway and busy road separating the pedestrian part from the actual riverside. In Prague, you can stroll along the very waterside and there's
swans. It's like they're cheating.
But seasons matter. In high season, Prague is infested with tourists. The above-mentioned areas feel almost like you're walking through some fair, at least on the main streets, its really not fun anymore. Probably got to do not just with the number of tourists, but with the ratio residents:tourists in a given place - Paris or London seem to absorb or disperse them better. Budapest rarely ever feels that way.
But in low season all thats much less of an issue.
Hmmm... ok.. <this is costing me trouble to say> .. if it's in November, just for the one day.. perhaps
Prague.