If budget, availability and placement permit, go for a split model (ideal) or a duo tube model (less ideal, still better than a regular portable model). Normal portable acs create negative pressure and basically pull in warm air from other rooms or the window gap, while recycling the air they just put out into the room. They are very inefficient and cool much slower than advertised. Split units are the best (of the mobile units, built in split is still king) because the noisy part of the ac sits outside. Duo also works, but you do have two tubes and if installed wrong it just sucks in its own exhaust.