Your choice of electrical generator really depends on how much output power you require and the type of supply, DC current or AC current. Personally I would go for a permanent magnet DC generator something similar from old buses and trucks, these generators/dynamos are more robust and operate at low rpm speeds. Don't choose a newer car alternator unless you want to install a gearbox as these require much high rpm speeds and an additional field supply.
In many ways hydro power is similar to wind power you are just replacing the turbines rotors with a waterwheel, so a similar type of generator would work fine for a small scale hydro system like yours.
Take a look at this site about, Small Scale Hydro Power
, They have lots of pages on the different hydro energies and waterwheels available and should give you some ideas. It helped me.