I'm a long time user of Auction Auto Bidder and can't say enough good things about it. On occasion, though, I have lost an auction because of some misstep on my part like my browser not accepting cookies or because of some of my experimental network settings.
Because I don't always trust my settings and depending on how badly I want an item I put my faith in AAB Online. It's never failed me. I recommend both products if you're looking for successful, trouble free bidding.