These are not really rivals - the SC2 Pro is a 25 Nm reference flagship, the Sport 9 a 9 Nm entry base, and roughly $350 separates them. Line them up and the Simucube wins nearly every axis, as it should at nearly twice the price: class-leading build, the best software polish in the class, and torque the Sport 9 cannot approach. It is one of the best direct drive bases ever made.
So this comes down to budget. If you can stretch to the SC2 Pro, it is a base you will not out-drive for years and the sensible flagship buy. If $399 is the number, the Sport 9 is a good place to start and the cheapest way onto Simagic's 21-bit encoder, with the ladder open above you. Decide which tier you are shopping in first - flagship or entry - and the pick follows from that, not from the rubric gap.