I've sold on ebay and it was exciting seeing those bids. Everything I listed sold except for one and of the auctions that sold I had one bidder not pay.
If you want to get rid of everything quickly, ebay is certainly the quickest assuming your starting prices are low. But listing all the auctions is very time consuming - especially if you add in detailed descriptions and pictures.
I preferred on-line payments because waiting for money orders before I could send out took FOREVER! But when you take into the listing fee, final valuation value, billpoint or paypay fees, and postage, you may not make much $$ per auction. If your item does not sell, you are down the listing fee and you will need to re-list. Of course, there the chance that your item gets bid up and you sell it for more than you expected.
After my last selling spree I got slightly burned out - checking everyday for bids, payments, e-mails, going to post office, etc. - and I'm working up my energy to make another go at multiple listings. I intend to take all the pictures and write up all the descriptions and save them to a floppy disks and list all the auctions all at once so they end at the same time.
In the meantime, I had listed a few things on half.com - mostly books & dvds - mostly items that I didn't think would sell well on ebay. I was surprised at the sales that were completed. It is definitely much slower and not for those that want instant gratification. But I liked the fact that it was much faster to list (no hmtl, pictures, or long descriptions), no upfront fees (so if it doesn't sell you pay no fees), that half.com collects the payment for you (no waiting to ship, no on-line payment fees, no non-payers. no e-mailing bidders with invoices, etc,), and that you get a shipping reimbursement that usually not only covers the postage but some of the commission fee.
Disadvantages are that you may wait a long, long time for your item to sell especially if there are lots of listings for the same item and your asking price is higher, the half.com commission is higher than ebay (not that much if you added in the ebay listing fee), and that you lose the potential for a buyer willing to pay much more for the item than you are asking for. Also, half.com only pays you once or twice a month depending on the amount of your sales, so they hold your money for a while, but I don't mind 'cause the checking account I have the payment credited to is non-interest bearing and I prefer knowing that the buyer paid.
Nothing to stop you from selling on both.
Half.com requires almost no work on my part except list occassionally, confirm my sale e-mails and send out the next day. I'm working up my energy to list on ebay again. I have a lot of stuff that not's suitable for half.com. But I'm not in the mood to clean, categorize, take pictures, write descriptions, and use html right now.
Good luck!