What are the pros and cons of water cooled vise air cooled?
this has already been discussed and answered frequently.
A summary of the advantages would be: Water cooling means reliable cooling independently of spindle rotational speed, Air cooling means not having to deal with plumbing.
What diameter spindle are you thinking of getting? I would only go with water cooled if using an 80mm spindle.
Big plus for water cooling is turn down (low rpms) since you are not relying on an axial fan for cooling.