I haven't been to the MGallery yet, but I think it's your best bet. Yes, the location is not the best, but it's not that bad either, you can still walk to the city centre, and it's next to several tram and metro lines, which is very convenient.

The Novotel round the corner from the MGallery has just reopened. The lobby and the restaurant are very grand, similar to the MGallery, but when I was there 3 years ago the rooms were very disappointing, as was the lounge - really poor. Plus the room was very cold in the winter. They have a sauna and a hot tub in the basement, but they seem to be closed at the moment.

Mercure City Center has a lounge, but at the moment it closes at 5 PM (!) and the offer is quite poor. The location is perfect, however, people have been complaining about the noise from the construction site next to the hotel.

For the past three years I've been going to the Mercure Korona. The location is very good, close to the city centre, but the service has deteriorated since the pandemic began. The last two times I was there they didn't even have slippers (in any room category), there was no welcome amenity, the pool was closed, as well as the lounge, which was replaced by the "snack time" (several canapes and fried nibbles) at the restaurant. Unfortunately, it's not the same and it's sad because the lounge used to be very good!
I don't know whether they have reopened the lounge since I was last there, but no one seems to mention it in the reviews on Google and TripAdvisor, so I guess they haven't.

The rooms are small at both Mercures and neither is on the list of the hotels offering free breakfast to Diamond members. I would personally go for the MGallery, but choose a suite with a courtyard view.