How to Choose the Right Slide (Excerpt from Acoustic Guitar Slide Basics) 

EXCERPT FROM "ACOUSTIC GUITAR SLIDE BASICS"
First, you will need to get a slide, and there are many kinds to choose from. You’ll need to try out a few different diameters, lengths, and materials to see what suits you best.
Most acoustic slide guitarists place the slide on their pinkie, leaving three fingers free for forming chords and fretting single notes without the slide. Placing it on your ring finger lets you grip the slide from both sides, with your middle finger and pinkie, but it leaves you with only two fingers free for chording and fretting without the slide.
Generally, the heavier the slide, the better the tone, with a higher “note-to-buzz” ratio. At the same time, a heavier slide is harder to manipulate-there’s more to move around, and if your guitar still has relatively light strings or low action, it’s going to take more finesse to keep a heavier slide from bumping into the fretboard.
But weight is just part of an equation that also includes what the slide is made out of.