You are going to find that most of the Forumites prefer plain edges. I tend to go your way with small blades being plain and medium being combo.
You can, as most here know cut fibrous materials with aplain blade by either push cutting with a thin edge or sawing with a rough, but sharp edge.
In smaller blades I like the plain blade because it is well suited for most intended uses of a small knife (envelopes, fruit, a string or thread here and there, etc.) and I don't want to "waste" vlauable blade length with the less than ultimate in versatility of a serrations.
In a larger blade, where I have enough plain edge to push cut cheese, slice an apple, perform food prep, etc. I like a small section serrated. Not just because of its superior performance on fibrous materials like rope (which most people do not cut much of) and cardboard, but because the serrated section gives you more cutting per linear inch of blade than does a plain edge (obviously) but because I can do the rougher, tougher, nastier things with the serrated section and still have a nice fine edged plain blade for the nicer, more delicate cutting and slicing.
Many will say here, and I agree, just carry two knives. A user/beater combo edge (or fully serrated if that's your thing) and a nicer and perhaps smaller, plain edge.
Looking at what I usually grab when staring at the knife drawer I'll pick either a Spyderco Endura or CRK&T M-16 (both combo edged) and the small Sebenza or the BM 940. The users are combo edged and the others are plain. Apples and cheese taste much better when cut with one of these great little knives but while they may be more than capable, the Endura or M-16 just seem better suited for cardboard boxes, (and the risk)catching staples), dirty work and rough work.
Carrying two knives makes sense. Multi tools and SAKs aren't factored into the math because they just "are."
[This message has been edited by Nimrod (edited 02-04-2001).]