"Best" is a relative term of course, as it depends what your priorities are!
When I bought my system a few years ago I looked around at what was on offer and there was a clear winner (if cost is no issue) and it was ionics zero system.
If I'd had the cash I'd have bought it, but it was out of my price range. I went for pure2o instead (ionics 'value' brand) and it has served me perfectly.
Not knocking any other companies when I say this, but having seen a few of them like grippa, X-line, etc etc they are all a bit 'Fred in the shed' compared to ionic. I'm sure they're fine, but there's no getting away from the fact that ionics are operating on a whole different scale to them.
If I was buying again, I would probably not get the RO and stuff in the van, I'd get a garage tank that was constantly filling and just top up the tank from it. One thing I would definitely like is hot water, so my dream system would be ionics thermo delivery system:
