I got to fire the Sten, MP40 and Tommy last year full auto 50 rounds each. The MP40 was very accurate firing bursts, almost all rounds were in the bullseye (even the American RO was impressed). The sten grouped well but not as good as the MP40. The Tommy gun was a pain to hold steady on target and cut a diagonal line from center to left shoulder of the target. Both 9mm's were very controllable.
Most of my full auto experience is with 556 but after that the 9mm has my vote for putting out accurate fire in bursts.