Probably the ROM 3. More onboard memory means that you will have more memory overall. The updated ROM should mean that less of the Toolbox is in RAM too, which is handy.
I think some suggest using ROM 1 machines for games. IIRC, a ROM 1 machine also allows you to put the SCSI card into slot 1 and configure slot 7 for appletalk. Which was useful for some long forgotton reason.