I have a specific tip for each of my attys in rotation. They're all 510 sized with o-rings, but the similarities end there. Tip selection is hugely important to the quality of your vape, and I'm glad to see others recognize that!
For my VA Cyclone (non-AFC, original 1mm bore), I use a nub tip with a super tight seal. This is my "cigarette" atty, with a tight draw and beautiful throat hit.
On my Immortalizer I need a little more of a buffer between the tip and the top cap, so I use a vase tip, again with an incredibly tight seal. The opening for this tip is heavily fluted and produces a spectacular, velvety vapour. This remains the only atty I've used that provides a "mouthfeel", and it just isn't the same on my other tips.
Finally, for my Freakshow Mini, I use a loosely fitted talon-style pipe tip. This is great for those long, hot draws, as it mitigates heat and sputter, and ensures I'm not drinking my juice. Not to mention it allows me to lean back and enjoy, thanks to the vertical orientation.
Anyway, my tips are all from Vape Stash, handmade acrylic on SS bits. They're gorgeous, but more importantly, they're intrinsic to getting the best vape possible from my attys.