Anyone stayed at AC Carlton Madrid on Paseo de la Delicias or Marriott on Gran Via? Which is better location?

Haven't stayed at either one, but know both. Location wise, the Marriott on the Gran Via, the Circulo Gran Via Hotel, Autograph Collection, would be better. it's for adults only, no children, and a bit more expensive.

Also look at The Principal on a side street off the Gran Via, a new design hotel.

I've stayed at the AC Recoletos several times. I liked the hotel and its location.

I am not big on Gran Via.
Stayed at AC Recoletos and my favourite (one street over..Jardin de Recoletos,
much nicer area imo

I've stayed twice at AC Carlton Madrid, the last time being in October 2016. Would stay there again. The location was convenient, just a short walk to Museo Nacional Centro de Arte Reina Sofía, Caixa Forum, and Atocha station, which was handy as I caught the train to Toledo, Valencia and Valladolid (on different occasions). It's also not far from Museo del Prado and Real Jardín Botánico, and just a 16 minute walk to Museo Nacional Thyssen-Bornemisza. It's also close to many eateries. Takes only about a minute to walk to the Supercor Express (a market), if you'd like to stock your minibar with refreshments and snacks.

The street it's on is busy, so if you'd like it quiet, ask for an "interior room." If you can, stay in a superior room as it's larger. They may upgrade you for free if they have rooms available and if you're Marriott members. They upgraded us.

I've also stayed on Gran Via in the past, but not at the Marriott.

I stayed at NH Paseo del Prado and loved it. Seeing the art museums was my mission and it was perfectly situated for that. Busses and taxis right outside the door.

Not familiar with either hotel you mentioned but as Diamantina wrote, the Carlton is closer to train station if that matters to you.

Another vote for the NH hotel - very convenient to all the museums as well as Atocha train station.