For my products, I get 94% using their mini-cart solution on my website, and 71% for sales they generate. You can increase your revenue with them by doing any of the following:
Link to Clickgamer from your website = +1%
... or link back to Clickgamer and put them FIRST in your list of TRY/BUY links = +2%
... or link back to Clickgamer and put them as the EXCLUSIVE TRY/BUY Link = +4%
So if you ONLY sell through Clickgamer you get 74% for sales they generate, and 94% for sales you generate (via mini-cart). Not bad at all.
Using their shopping cart on your site gets you 80% of the revenue. Otherwise you get 60%. Handango generates a ton of sales, however. Even after switching to Clickgamer's mini-cart, Handango still generates five times as many sales as Clickgamer. Before switching, when I was using Handango's solution, it was about eight to ten times as many sales. The increased revenue from Clickgamer seems to offset the fewer number of sales I get through Handango now, however, and Clickgamer is a delight to work with.
For my $9.95 games I always seem to get $5.53 from them, so that's a sorry 55.5%. They take 40% + processing fees, and you absorb any fraudulent chargebacks or returns. I once actually received a negative statement from them for a couple of bucks. I just waited until the sales for the next month covered it. (That was a few years ago with only one product on their site, so now it's not really a problem.)
Since the only source of PayPal sales comes directly from my site, there aren't many sales made using it (especially since I also give links to Clickgamer, Handango and PocketGear). Anyway, in 2007, 1.46% of my sales were through PayPal, but that was 2.75% of the total revenue, which speaks quite highly for the percentage you receive when you use it. Selling the Collection Bundle from my site for $14.95 produces $14.22 in revenue, which is a 95.1% return.
I haven't tried any other portals. I'd rather spend my time making games than doing the administration work. Hopefully this information helps.