Aftermarket block or factory block? What kind of racing?
I've used a little of everything. The FM bearings are nice and will drop right in. If you have an aftermarket block that uses a Cleveland bearing, and you use something like a Clevite, ACL, or King, you will most likely have to cut the thrust bearing flange down.
I use a lot of FM bearings, but I also build engines where I use coated bearings and usually reach for the Clevite HK series stuff.