How do you choose your components?

Obviously, you're first probably going to do some research to find parts that meet criteria you need (for example, an LDO regulator with low drop out voltage to minimize loss), or a capacitor with a higher voltage rating than another one.

But what about manufacturer/part/etc? Say you've got a part my ON semi, Micrel, Maxim and TI. Datasheets are similar, features are the same... What makes you choose one over the other (forget about any cost differential for a minute).

Second question: Do you/have you ever chosen "multicomp" over another brand? stocks parts by "multicomp" which as I understand it is just a variety of companies lumped into one, but given say, a ceramic capacitor. All things being equal, would you pick mutlicomp over Kemet/another brand?

I'm still learning about circuits and such, but when I go to pick parts for my projects, I can't always see a benefit to one vs the other ( an 8pin header by multicomp is the same as an 8pin header from say, Tyco..."i mean it's plastic and metal right?, so why is tyco 60 cents more" kinda thing).

Of course the answer is "It Depends".

When choosing between name-brand manufacturers like On Semi, Microchip, TI, etc., price wins if everything else meets specs. OTOH, I've had good luck with the "Various" company as well, especially for the items that are more commodities like voltage regulators, diodes, etc. The more specialized components will tend to be sourced by fewer manufacturers so that naturally limits choices. Sometimes physical size wins with things like capacitors. If you're just a hobbyist like I am, then surplus parts can be a good value, but if/when the supply dries up, then physical size or specs can change which might be an issue if you're doing higher volumes. If all else is equal including price, I will favor a known brand name over a no-name (multicomp, various, etc.) part.

Can't say that I've had any quality issues with anything I've bought recently, whether brand names from Mouser or Digi-Key, surplus from various suppliers, or parts from sources in China or Thailand.

One resource you might like is the EEVBlog:

He's had a few episodes about component selection and circuit design.