I have a twin AK4040 pumped system but from what I hear the new HF5 is the business, no need for a booster pump, very good quality water and very high production rates.
The AK is a very good membrane but really needs a booster pump to get the most from it (i run it between 80 and 100psi), if I had to choose again I would go for the HF5, apart from being cheaper than an AK + booster pump there is a lot less to go wrong.