The ninja offers the best spec, but i have heard there aftersales isnt great
I have the excell and its a decent machine but im thinking of upgrading to the ninja, so i may be selling the extracta soon if your interested in a second hand machine.
Any manufacturers chemicalls will work in all the machines, and most places that service or repair machines or sell parts will be able to fix and supply parts for most makes, so dont tie yourself to prochem just because you have a distributor near you.
I own the extracta excell, and have had it repaired by alltec and woodbridge
Another model that might be worth considering is the (mytee speedster) good spec and good price, i know nothing of reliability or the after sales but its worth considering as its a better spec than the prochem, alltec, and extracta and only about £1300.
Try matt at cleansmart, or woodbridge for details