I like Unearthly Child (as a stand alone episode), I wish it was entitled as such and the remaining three episodes remain separate (as a Tribe called Gum), because they were so different, & besides I find the remaining 3 boring.
Just watched "The Daleks" for the first time a few weeks ago -what a superb first episode -really up there with some of the best. I think the bulk of the first season's $'s must have been spent on this story.
The Dalek Invasion of Earth is okay, but I think maybe a little too highly regarded by some. Personally I prefer the movie version. Maybe I prefer it as I saw it first and it is really a copy, but with a bigger budget. I don't know.
I like the Aztecs, The Time Meddler & The War Machines too, these are good solid stories. There's a couple I'm yet to see (half way through "The Sensorites" & yet to watch "The Web Planet" or "The Tenth Planet", will get to those in the coming weeks).
But of the ones I've seen, my favourite is "The Ark". If you look beyond the look of the Monoids (which I thought was rather clever), the "Security Kitchen" & Dodo (a companion who tends to rank near the bottom of "favourite" companions rankings), it is a well paced, great story with a nice twist half way through.