Harry Weisfeld does a great job of continually improving his turntable designs, with each generation showing better performance that its predecessors.
The Scoutmaster is the newer design, so presumably it should offer better sound quality (particularly if you get the Signature 9 arm). It also offers the peripheral ring clamp, which is a great device. If it were me, I'd buy the Scoutmaster, not the original Aries.
However, if the comparison was between the Scoutmaster and the Aries 3 with the longer arm, then I'd choose the Aries 3.
The Scoutmaster is the newer design, so presumably it should offer better sound quality (particularly if you get the Signature 9 arm). It also offers the peripheral ring clamp, which is a great device. If it were me, I'd buy the Scoutmaster, not the original Aries.
However, if the comparison was between the Scoutmaster and the Aries 3 with the longer arm, then I'd choose the Aries 3.