Agree with all, maybe I put Blink at no 1.

Blink. Awesome creepy atmosphere mixed with cool new creatures.

David Tennant's finale, The End of Time. That episode was a deconstruction of the Doctor Who persona. 

It's everybody's favorite, but Blink.

Waters of Mars, it was so dark I love it.

Disclaimer: I've only watched from the start of Christopher Eccleston's tenure to about halfway through Matt Smith's tenure (think the final series I bothered watching was the 6th, where things started getting horrible).

My favourite episode, by a country mile, would be "The Girl in the Fireplace". Hits a great emotional note; has a fantastic sci fi/historical setting melded into one and is just an all-round fantastic example of what the show could me. And made me a massive fan of Stephen Moffatt after that.

It's a shame he couldn't keep that level of quality up as showrunner.

I suggest you keep watching. Maybe this is the fanboy in me speaking, but the season finale of that season was quite enjoyable and I think that the Silence are an extremely interesting villain (albeit criminally underutilized).

Also, if you get through it, you get a new companion and push on a little further and you get a new doctor (the tone of the new doctor changes the series dramatically imo).

While the show did change a lot and I don't think it is as good as 9/10, I certainly think that its still worth watching ^.^

In no particular order

Blink

Midnight

I do feel like I'll probably give it a try again some day, but I begun to lose interest as soon as Moffat became showrunner really.  His teasing at the end of S5 - providing a mystery that wasn't going to be solved any time soon - actually turned me off the show more than made me want to continue watching.

Then during S6, the mid-season finale (A Good Man goes to war) was hyped up at this incredible battle that was in fact a damp squib.  And then the show returned a few months later with a stupid gimmick episode (Let's kill Hitler) that was supposed to tie up a really important storyline (River Song).

After that I've only watched periodically - Angels Take Manhatten; that episode with John Hurt in etc.

Haven't watched any of Peter Capaldi's episodes yet.  I'm sure they're fine, I just don't have the same drive to watch during the Russell T Davies years.  He may have been a bit of a hack writer, but at least he could create a big mystery and then tie it all up within the season to keep me interested.

Agree with this too, liked end of time too.