Best Clapton, to me, is Detroit Ballroom, Fall '67- Cream were at their peak live. Sadly, this is not an authorized release. I wish Clapton would legitimate it-- it is purportedly a board recording, but there are at least two different versions. I hate getting behind a bootleg, but it is there as a piece of history.
As to best "first tracks," I dunno. I listen to a range of stuff, from early heavy rock (now often called "proto-metal") to jazz. I have a visitor tomorrow and was thinking about what to play. I have a lot of records, but got out of the habit of a "short list" of regular players for demonstration purposes.
And, I'm more into jazz these days than hard rock, but I can dig a psych or heavy rock album for sure: Lucifer's Friend (German Philips the album with Uncle Fester); Crimson- Toronto 2016 Live- Starless; Art Lande And Rubisa Patrol– Desert Marauders (killer jazz record that has an edge; well known cheap heat); Chris Whitley- promo version of Living with the Law-- a/k/a National Steel- fewer cuts, sonically nicer. Standard issue Columbia.
I'm sure I'll play more tomorrow- but part of it is what the guest likes, no?