I would have to say Once Bitten, and I'm sure almost everyone here can agree with me that Once Bitten was a FAR better episode than The Splinter.
And I also think that this episode should have just stayed as is, meaning this should have been the only episode produced involving splinters, rather than having another splinter episode that was putrid, vile, disputable, atrocious, degrating, and one where it had a very pointless and foolish plot. (Which is The Splinter.) I may be exaggerating but still, I think at least some of it is true (what I just said about this episode, like putrid and pointless.)
I'd also say Once Bitten was more well written too, example: Did you notice that it was much easier for the splinters to be removed in Once Bitten? And they also didn't turn into a red and nasty monster? I did.
Once Bitten is likely to win this poll. But I just wanted to see what kind of reactions and results this thread/poll would get.