Best place to stay in Eger

We stayed at the Senator Haz Hotel 3 nights last year. I was at first surprised when they showed us to our room which was in a separate building a short walk from the Square. But it was nice. More modern, larger and quieter than it probably would have been in the old hotel building.

Everything is very close together in Eger- the square, the castle. I enjoyed Eger more than Budapest. Do go to the thermal baths. My favorite experience was visiting the marzipan museum, just amazing art made out of marzipan.

We stayed at the Senator Haz. Our room was in the main building. As I recall, it sits a bit off the main square but quite close. Our visit was in late September, but I wouldn’t describe the square as busy and noise was never an issue...and I’d say so because I’m rather sensitive to noise and especially at night. The breakfast was fine, and when I asked about laundry facilities nearby they arranged to have our laundry done for us...dropped at the desk and they returned it to our room. As posted above, it is a small place and everything is pretty close to everything. I doubt it was more than a ten minute walk to the castle. I recall a nice meal at the Cherry Etterem. We spent two nights and full days in Eger and it was sufficient for us. Safe travels!

We stayed at Imola Udvarha for two nights this past Spring, and I am happy to recommend it. Yes, it's a little removed from the main square, but it's a really pleasant and easy walk down to (and back from) the square. I'm not sure if it's any quieter than it'd be at Senator Haz, though, as there's a lot of foot traffic going up to the castle complex right there as well as what seems to be a commuter walking path up and behind the hotel. There was absolutely no noise at night, but we could hear people starting at 6am. That said, we had the windows open as it was a warm May night.
The hotel itself was very pleasant. We had a two bedroom apartment with a small kitchen -- both beds were extremely comfortable, the bathroom was large and easy to use, and we loved just relaxing in the small living room area. Our room was immaculately clean as was the entire hotel. Also, the breakfast was really quite stunning, and we loved the bar attached to the hotel. Our travel agent had some language barrier issues when making the reservation for us, but when we were there, we were able to communicate without any real issues. Anyway, I hope this is helpful. We adored Eger and hope you do too.

Since james.august mentioned open windows, allow me to point out that I needed my air-conditioned Budapest hotel room in early May 2018. (I don't know when your trip will take place.) I don't know whether Eger's weather is similar.

Is one day enough to see the sights in Eger?

Morning train up, spend the night, last train out the next day is probalby enough to make the trip worth while. With vineyard tours and wine cellar tours you could do a few more days. Senator House is the right place if you can get a room in the old building.