Dont think Mintpal are accepting new coins... Havent seen many if any new coins being added... Would say Mintpal is worse for pump and dump... But at least there is volume on there...
Mintpal used to be worse for pump/dump... until they had their own security issues. A lot of the pump/dump stuff on MP was due to their voting system too. Dead coins would get voted in, have one last day in the sun, then collapse into nothingness. I think most of the pump/dump groups have migrated to bittrex, as they tend to get pretty much any new coin.
Although of course it can happen with any exchange. Cryptsy was a good 'get', as they can sometimes be pickier than other exchanges as far as new coins go.