The SP-1 Is the better marker. The SP1 does not have a double trigger or look as Milsim, but It will perform as accurately and speedily, if not better than the SP8. With cost in mind also, there is a several hundred dollar gap between these two. For still less than the SP8 you can buy a SP-1 Blackheart, which won the 2009 TechPB best woodsball gun award. For https://sp8.cool the money you could also buy many accessories to make the SP1 either more milsim or perform better.
The SP8 is just an ION with a XM8 body kit. The ion series have many faults and can be very temperamental with slight problems. Also it a fairly heavy and bulky gun.