AI'm making a single tier, three layer fondant covered cake. I want to have a lemon filling and a raspberry filling. I've already made lemon curd and a raspberry sauce. I want to fold them into the icing to make the fillings. I was wondering which buttercream, imbc or abc, would be better for that. Also, if it matters I'm making the cake today (Wednesday) and serving it Saturday night. I would appreciate any help or opinions on this. I'm about to make the buttercream now and I can't make up my mind which one lol...thanks!

I think I'd go with the IMBC over the ABC.  I used to work exclusively with ABC, but now that I've been working with SMBC, I like it better, tastewise, but it's still a lot of work.  So for personal consumption, I'd go with the meringue buttercream.

Although, I think it would taste better with just the curd or filling by itself and not mixed with the IMBC.  But that's just me.

This is a matter of personal tastes.  I do not like IMBC and would use either straight filling or abc

I'm another one who doesn't like IMBC, taste-wise.  I also don't care for it's stability (or lack thereof).  I use IMBC upon request and only if the cake won't be subjected to a lot of physical stress.  I'd be scared to death to put it under fondant, but I do know other people do it all the time.  This is one of those things where I think it's better to do a few experiments and find out what works best for YOU.