The ASEL checkride must be done in an ASEL. There are some maneuvers for that rating which do not apply to AMEL (ie engine out approach to LDG and some ground ref manuevers).
If you have a reasonably assured job path to an MEI job then you could skip the ASEL. But if you're going to apply for random CFI jobs, those will always have new CFI's start in ASEL, and work up to twins when they have more experience ( and their senior MEI's leave for the airlines).