Nemzeti

pro : Nice hotel - good status recognition
con - Bad area ( but not that bad ) - no lounge - avoid some of the rooms in the front ( small / noise )

Mercure

Pro : good recognition - normally full of "tours" - simple small lounge - cant really "make a meal" - but you will be eating elsewhere anyway. Pay for breakfast as the lounge was not equipped
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Con : small rooms - busy hotel

For my 2c worth the Mercure is best "value", but the Nemzeti is a better hotel.