Leaving the water splash photography completely out of the equasion, any one of those heads will do the job for portraits and photographing children, but in fact will be overkill.
Fashion photography - true fashion photography with lots of movement that is - sets higher equipment standards and in my view leaves your choice between the Elinchrom and the Lencarta. Both have incredibly fast recycling, which is important, and both have extremely accurate and consistent colour temperature consistency, which is equally important.
When it comes to water splash, or anything even remotely similar, the Lencarta SuperFast is in a class of its own. The only other flash head that comes even close is the Alien Bees Einstein, which is much more expensive and which also isn't imported or serviced here in the UK. But, bear in mind that I'm not impartial, because of my association with Lencarta - but this association does mean that I have thoroughly tested every single flash head on the market, so know something about them - and the same goes for Richard, who posted earlier, because he is a technical writer for various photography magazines and he too gets his hands on a lot of different equipment.
It's difficult to say with any precision (because the speed needed is very much dependent on both magnification of subject and direction of travel) but I would say that the minimum shutter speed (continuous light) or flash duration (flash) needed to freeze movement is around 1/3000th sec, so that's a t.1 time of 1/3000th or a t.5 time of around 1/9000th, if that helps.
The advantage of getting a really fast flash, other than interest in photography, is that having one will allow you to get the sort of shots that other people simply can't get. Only you can decide whether that's the path you want to go down.