I prefer that NPC's and PC's work according to the same rules (or nearly so). For example, if the PC's have triple hit points, then all the 1 HD NPC's would have triple hit points too. This would be wierd IMO. So I prefer 1st level characters to be 'fragile' whether they are PC's or NPC's. If I want starting PC's to not be fragile, I'll start them as 3rd or 4th level characters.
Of course, fragile is a relative term. I've always found d4 classes to be too fragile at low levels. In fact, I can't ever remember a pure wizard that survived past midlevel in any game I've ever played or ran. And adventures for 1st level characters are tricky to run, so I empathize with people that find 1st level characters too fragile. I've generally either put kid gloves on or else made everyone start with two characters, and neither is a perfectly acceptable solution.
It's not really the fragility at low levels that bothers me though, maybe because I'm used to it. It's the fragility of characters at high level that bothers me.