We went posh, if you can stretch to it the Hotel Lord Byron is in a very nice part of the city overlooking the Villa Borghese(big park just north of the centre) and the food is amazing. The standard room walk up prices can be ridiculous but there's plenty of offers on booking.com and the like where you can get a 4 night stay for two for £400ish. We stuffed our faces at breakfast and didn't have to eat again till 4. It's worth it to get a bit of luxury, especially if you're with the missus, you won't be disappointed. The 'budget' hotels around the spanish steps aren't that much cheaper, you're paying for the location.
Winter is a great time to go, we went in December and had a great three days.