While Prophecy Girl is a great ep, Angel is by far the best because it is so pivotal in the whole Buffyverse. From this ep on, the lives of Buffy and the Scoobies take a sharp turn and this is when the show really takes off. Beforehand, we were trundling up the incline at the start of a rollercoaster.

'Angel' was the first white knuckle drop....

Prophecy Girl
Buffy dies! - What more needs to be said

Angel was always my favourite for season 1 followed closely by The Pack.

Just as an aside, there is no 'Welcome To The Hellmouth: Part 1'. Just 'WTTH' and 'The Harvest'

I voted "Angel"

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by Taz
Buffy dies! - What more needs to be said

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But she come back to life

Oh yeah!
Damn!!

Angel by a mile.

I also liked Never kill a boy on the first date, and Out of site out of mind, which was a brilliant Cordy ep.

Welcome to the Hellmouth, Angel and Prophecy Girl are by far the best episodes.
The rest were OK to fair, but each one usually had 2 or 3 excellent scenes and fabulous humour scattered through them.
I think Prophecy Girl shades it as the best, even if its just for:

The Master: "You are Dead."

Buffy: "I may be dead, but I'm still pretty"

TM: "You were destined to die. It was written."

B: "What can I say, I flunked the written!"