Tielfings are my favorite race, so I'm about to go on a rant here. But I don't really understand the poll because I can't figure out if you are asking if I prefer those Tieflings, or if I prefer to see Tieflings appear in those books. Cause I believe the Tiefling didn't come out until 2e Planescape and there is no Tiefling in the PHB/DMG until 4th edition. If it is about which book, I would rather see them in a planar book than as a core race in the PHB. I just don't think they belong as a "core" race. I mean, a fiendish race is now core, but a celestial version (Aasimar) is not? That's nuts, but I still prefer neither to be core. "Core" to me always meant "vanilla". A tiefling, half robot, or half dragon just does not scream "vanilla" fantasy to me.
For those not familiar with the 2e version of the Tiefling, it started out with a generic set of racial adjustments similar to the 3e version. Since the background behind them though is that "Tieflings are half human, half unknown fiend, and no two ever look alike", you could replace the generic racial adjustments and use a set of charts to select your own set of racial adjustments along with racial features. Or you could roll randomly for these, or make something up if the DM allowed it. There are even racial side effects that could really spice up your character without giving any real in-game advantages (like casts no shadow, smells like sulfur, prolonged touch withers normal plants, etc). Since none look alike, the racial features are almost limitless if within bounds. You don't want the 4e style horns? Take some rhino horns instead. How about a reptilian tail? Or maybe two lion looking tails?
So I prefer the 2e Planewalker's Handbook Tiefling. I don't know why, but ever since 3e, the designers just seem to throw flavor out the window in order to focus on stats. Wanting to roleplay monsters and grabbing my 3.5 Monster Manual to read up on them is depressing. I rarely get any useful information and I end up going back to my 2e books to get fluff.
They butchered Tieflings in 3.5 (and I run a 3.5 game). Then 4e came along and made them even less interesting. I really don't understand why they deviated from the 2e PS concept. It provides players with so much more opportunity to create an interesting character. It even would allow players who like the 4e version to still create that exact Tiefling if they wanted to. So I use 3.5 versions of the random Tiefling charts in my 3.5 Planescape game. I also use a very similar chart for my 3.5 Aasimar since they are the half celestial version of the Tiefling. Their racial features are more celestial looking (golden skin, covered in white feathers, melodic voice, etc, etc).
Here is how I prefer my Tieflings to look (and I really don't like the art for the 5e PHB Tiefling...how uninspiring):
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