Hot press is super smooth without any texture. The pigment or water will not be absorbed as quickly as cold pressed, but instead will tend float on top of the paper, allowing you to play around more, like re-wetting edges of pigment. If you plan to add pen and ink in your process this would be a good choice.
The weight of a paper is also something you should also think about when choosing your surface. A light weight paper will buckle with water or pigment that is added. If you work very wet, you will want to use a heavier paper.
The importance of acid free or archival paper cannot be stressed enough. Have you ever wondered why old newspaper clippings tend to yellow with age? As an artist, if you want your originals to look as clean and crisp as the day you created them for all time, choose acid free paper.