It's a no-brainer for me, I use the ERR Cruise Commander and an appropriate ERR RailSounds Commander kit. For steam, you will need to address the chuffing and managing the smoke unit. Of course, I use my own Chuff-Generator and Super-Chuffer II for this task.
As Pete says, the PS/3 upgrades include managing the smoke unit and generating the chuff signal. You do have to have a compatible smoke unit for PS/3 upgrades for proper smoke operation.
If you run both DCS and TMCC/Legacy, the PS/3 upgrade will be cheaper overall. If you strictly run one of these command environments, your choice is obvious.
