Aha, finally another slippy strap lover like myself. I hate a grippy strap pulling at your clothing all the time. I like to be able to slide it around.
I've found the Mono Betty to be my favourite. Wide, padded, strong metal fixings and not grippy.
They do seem to to have leapt up in price, I'm sure I only paid about £30 for mine, but it was some years ago, but there ya go, they last for years.