If you're doing something like

E| 15-16-18

Should you do fingers 1 2 and 4? or 1 2 and 3? Many people seem to use the first three fingers, but it's awkward to try it like that.
When I try and use the pinky though, it's difficult enough as it is creating the proper sound perfectly
Do what feels comfortable, and ignore the pinky police. Sometimes it's nice to not use your 4th finger in such a situation, because then it opens up possibilities of some four note per string ideas.
I always try and use the fingers that would apply to a scale, or at least fingers that would correctly fit into a box pattern. My suggestion would be to practice exercises that strengthen your pinky so you get a good, defined sound.
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Quote by deaththrashcore
Do what feels comfortable, and ignore the pinky police.

This + 9001
Q: Favourite Pink Floyd song?
A: The one where they get wicked high and play Emin and A for an hour.
depends on the context. Where'd you come from, where you going next? There could be situations where one or the other fingering would be favored. Don't limit your options practice it both ways.
You should use your pinky. True, in certain situations (depending on what comes before/after the lick) you might want to use the ring, but that's the same all over the fretboard.
Speed is a by-product of shut the fuck up.
If it's just those three notes without any higher or lower notes on the same string immediatly after, use whatever is most comfortable.

Using the pinky is important, but on the higher frets many people including me find it more comfortable to use the pinky for the 5th+ fret above the index instead of the 4th+.
Honestly, you're going to want to be able to do whatever fits and feels best at any given time. That alone should be your long-term goal.

So if you're just starting out, I would recommend nailing the most basic fingerings first... i.e. one fret per finger or in this case 1-2-4. If you cannot play that... you should probably not be jumping ahead to quick fixes... that's just avoiding a most basic concept - and paving the way for weak spots in your ability down the road.

So I'm not saying you ever must use the pinky I saying you should be able to. Big difference. If you only do "whatever feels comfortable", that's good for now, bad for later.