Firstly, I have only used AuctionStealer, so my opinions are limited to this auction website. I did consider jwalker/jbid or whatever its called, but given that auctionstealer is website based, and free for 3 auctions a week, I used this.
Advantages: 1) website based which means you don't need to be at your computer to bid, and you can log in anywhere to alter bids 2) never misses, at least not when set on 10 second free sniping, and paid up 3 second sniping 3) group bids together so that you don't win multiple versions of the same thing 4) bookmark add on to add items into Auctionstealer from Ebay 5) free for 3 bids a week, or USD12 for one month subscription, which means you don't have to sign up for a whole year, and only use it when you really need to 6) simple interface, no stupid adverts for other rubbish you don't want to look at
I almost don't want to leave this review, as its going to give other Ebayers a similar advantage. This software has transformed my use of ebay.