So I have always used AMBC but finally found a SMBC I love. My husband still prefers the AMBC so I am not conflicted. I really want to change my business over to SMBC as I have received comments that my icing is too sweet or gritty characteristic of SMBC but I am worried if people will truly prefer this and it will increase my booking rate for wedding cake tastings?

Any advice?

Could you not offer a choice of either to your clients for any cake you make?  

I would offer a choice. I've had people request American buttercream before but I mainly use SMBC for all my wedding cakes. I talk about the gritty mouthfeel of AMBC at tastings and people tend to love the SMBC. 

I would offer a choice except noone in my area seems to know there are different types of buttercream....and explaining it becomes a pain

I agree that offering a choice is your best bet.