Best "tip" is that it doesn't make any difference. Play with the tip that gives you the feel you want from your cue. If the feel is good you can get all the english you want (and more) from a soft, medium or hard tip.
I use an UltraSkin Pro Soft, one of the softest tips available. But it's because I like the way it makes my cue respond. I'll often play out a rack with my break cue (Samarsa tip; the hardest leather tip on the market) and can get the same amount of english. It's just not a feeling that I want intermediate or long term.