I started out using my middle finger...moved to ring finger...and then back to middle finger. Story behind it?...I play with a really thick, heavy metal slide and the weight distributed the best on my middle finger. However I discovered I couldn't get quite as far down on the neck for really high notes so, to the ring finger it moves. Then I realized I could hit any high note I wanted just by turning the slide at a diagonal instead of feeling like I had to keep it perpendicular to the neck the whole time...duh! There's a lot to be said for using the middle finger too! It is the LEAST used finger on your left hand for chording, etc. therefore, it doesn't take anything from your playing when you have a slide part in a song. You will have a whole bunch more control using your middle finger and the slide won't just fly off from your finger either like it can on the ring or pinky fingers either. Try it! Don't worry about any right way or wrong way to do anything either....make your own rules and don't be afraid to change or break em along the way!