in brief
04 , tarted upgraded from the speed,has a sensi rod ie if no ball touches the rod gat wont fire,but you have to calabrate it,a lot of people did not trust it,but if you calabrated it i found it fine
a4 meant to be the lightest angel ever(at the time) more firing modes, sensi rod as well
05,smaller and has eyes,ie if a ball does not break the beam of light it wont fire,more reliable than sensi and now standerd
you missed out the euro,released for europe only,after the a4 but just before the 05 and has eyes.imho the best out of the lot shoots flat like a cocker but with the speed and reliability of a angel,prices are silly cheap as well up to £500 of last years price,second hand