Any of them will work, basically. I prefer Enhanced Water, but Phinix Waterfix will work too. Just try them, and pick the one you like best. We, honestly, cannot make that choice for you. Some want clear water, some want bright blue/green water, and others want muddy water... Other options are Natural Water and Better Water? and Improved Water? I'll stop with the listing that I am failing at and give you a search by number of downloads, descending at TESNexus. All of the favored mods are on the first page... except for Enhanced Water HDMI I suppose. It is kind of new, and it basically combines Enhanced Water with the SI add-on and makes the water somewhat clearer (which is what I do not like about the update.) Oh, and Phinix Waterfix v2 might not be there either. I did not check, but there is an updated version of Phinix Waterfix now.
Most downloaded "water" mods: http://www.tesnexus.com/downloads/search.php?name=Water&scid=20&author=&mname=&desc=&size1=&size2=&downloads1=&downloads2=&udate1_day=&udate1_month=&udate1_year=&udate2_day=&udate2_month=&udate2_year=&ldate1_day=&ldate1_month=&ldate1_year=&ldate2_day=&ldate2_month=&ldate2_year=&endorsemants=&images=&readme=&advltonly=&page=1&orderby=downloads&order=DESC
Edit: Plus, someone just asked a very similar question. This thread is on page 2: http://www.gamesas.com/index.php?/topic/1102694-which-is-the-best-water-mod-that-doesnt-impact-performance/