Lively hotels can be found generally in Marmaris City Centre
More laid back hotels can be found in the Armutalan area at the back of Marmaris where the local council has banned the playing of music after Midnight. Armutalan council has also banned live entertainment from bars limiting it to hotels.
There are exceptions however so make sure you choose a hotel that suits you.
As with any trip it is advisable to check websites such as trip advisor, for info on your hotel before you book as there can be great differences. All inclusive deals are good value but beware of bed and breakfast and half board as hotels may restrict you bringing food or drinks into their premises making you dependent on their offerings which will be much more expensive than buying from a supermarket. In a very hot climate like Turkey a few drinks each day can add a lot to a holiday cost. In self catering properties beware of damage charges. Soiled towels and bedding can cost up to 80TL to replace and damage to curtains and furnishings can be very costly. Note any damage however small on arrival and report it!