We used to visit Cardiff a lot and our favourite hotel was the St David's: but it's a few years since we've been, so don't know if it's still as good. It's down at the Bay, not in the city centre, so not so handy for the city centre sights - but the buses & trains are good & it's not that far to walk. We particularly liked the balconies, separated by canvas 'sails', which give the feeling of being on a ship heading out to sea.

For somewhere a bit different but out of town (will you have a car?), I've heard good things of the Llanerch Vineyard Hotel & hope to stay there myself one day.

Llanerch looks lovely! I contacted them and they suggest either a train and then a 2.5 mile cab ride or a bus that comes directly. Will look into it. If it seems too difficult, St. David's looks like a good bet too. Thank you.

Part depends on what you care about, location-wise. I haven't stayed at the St. David's, but it's both a nice hotel and well-located for an evening hanging out around Cardiff Bay. I have stayed at the Radisson Blu (eh), the confusingly-named Best Western Plus Maldron Hotel Cardiff (right next to the train station, nice and new, otherwise unremarkable), and the Hilton (quite nice, good for access to the city center and Castle, worth paying extra for an Executive room with access to the Executive Lounge with views directly at the Castle). My favorite as a hotel is the Hilton; my favorite as a one-night stop between train trips is the Maldron.

I've also stayed at the Hilton, Jury's Inn, Novotel, Mercure, Ibis, Big Sleep & Jolyon's - and liked the St David's best (but it was the most expensive!) I positively disliked the Big Sleep & Jolyon's, and while the Mercure was quite nice for a budget choice the location is very inconvenient. The others were fine for their respective price levels.

P.S. Moosebear - useful to know Llanerch may be doable by public transport, thanks!

Thank you all for your interesting input -- very useful. Caroline_edinburgh, what was it about St. David's that makes you like it more than the others? (Since this may be my one shot at Cardiff, I want to make the most of it!)

Years ago I stayed at Miskin Manor, which is outside Cardiff, very near to the M4 so not sure if that location is convenient without a car. It was very nice, esp the restaurant and grounds.

I too like St David's, great location.