The best ones to have are the evacuated tube type,but he will also need a solar controller to make things run efficiently & a circulating pump pressure relief valve,auto air vent,pressure guage,various isolating valves a pressure vessel and a new twin coil hot water cylinder.
the firm i've been installing for use german made panels (5 year warranty)
also he needs to work out if he has a south facing chunk of roof (ideal situation) otherwise it means fitting panels on east and west facing sides (which means more panels & an extra pump) The'll sell him a south facing kit (all parts mentioned above + some other bits) for £1907 inc VAT
they are Global energy direct.co.uk not a job for the non-plumber,the system is filled with quite a strong mix of ethelyne glycol which Will find all available opportunities to leak ( this has been learned the hard way). if he wants someone to fit it give me a shout e-mail in profile