Modem/Router combo units vs. stand-alone modem + router?

Which came first--the chicken or the egg? :D

I prefer separate units because I think they are easier to trouble shoot and because I prefer to only replace one function when it fails. Other people prefer the combo units because, I guess, one mysterious "box" seems preferable to two mysterious "boxes."

The recommended coax cabling is to have one high quality two-way splitter. One half goes directly to the modem and the other half goes to everything else (with additional splitters if needed).