What it "should" be, and what it "will" be are almost certainly two different things. A bit like when the Hawk T2/Mk128 was procured...and look how that turned out.
Realistically, there are 3 options. T7 (which is unproven and the USAF aren't entirely happy with it yet). M346 which has been in service and proven by NATO allies. Or T50, which is the most capable but not yet as well established as the M346.
I'll bet we get the Hawk T3...