I use several tunings, depending on the song. I taught myself
slide after many years of failed attempts. Fortunately, I did it in natural tuning, which allow me the be very comfortable playing slide anytime to mood strikes me in any song.
Even though I play a lot of electric now, when I was younger I was more of a 'folkie' so I was also pretty familiar with dropD, double dropD, and open G.
I learned open E later to do the Duane type stuff.
It was Kirby Kelly who showed me that open G was the same as open E except everything moved over one string. that was a real revelation, because it meant all the licks I had learned in those two tunings could easily be adapted to the other just by thinking 'move everything over'. Now I don't think about it - its automatic. So that gave me open G, open A (G tuned up one step) Open E and open D (E tuned down)
After seeing Sonny Landreth a few times I've been fooling around with open Em and open Am which is so easy to get into-you just tune the third down 1/2 step. On electric, with a touch of reverb and light delay you get that real moody melodic spooky kind of sound. Last night we were playing 'Love Potion #9 in minor tuning. If you know the song, try it in Am tuning. Its cool.
But my favoritte is probably open G or A depending on the range I'm singing in. I like the way the riffs fall with all those 5ths everywhere- you can go country or very bluesy depending on your choices. Thats also wehre most of my vocal range falls so I sing a lot in those keys.
b.