It's been a combination for me up until last September. I had a totally blank template with everything bulldozed and all premades deleted. I also had a template with all empty houses bulldozed, premades modified, some kept, some deleted and only one each of every type of venue. Both of those templates have since been deleted.
I now use a totally new custom template I made for any new save game. This template has almost all empty houses bulldozed, except a few smaller ones that I like, most premades still reside in their original houses, but they've all been modified a bit. I also added in all my favorite Sims from other saves and NPCs/Townies I've saved that I liked. They're all townies now or NPCs not in world. I like seeing my Sims wandering around or working in different NPC roles and I like knowing exactly who will be my mail person(s).
I still don't interact with premades very much. I might use one now and then for a spouse or love interest though. But I mostly just use my own Sims I put in this template for those purposes and concentrate on my main Sim(s) created for that particular save. Sometimes I'll put my main Sim(s) in one of the empty houses I kept, but 9 times out of 10 I build them a house after they've earned simoleons for one. I love starting out my Sims on an empty lot with no funds Rags to Riches style. :)