I am the proud owner of both scripts, both are very nice scripts, the rearrange thumbs via ajax is really nice with gallery daemon.
The thing GD lacks is the ad system, you have to upload the ads, then create advertisements like so
Code:
<a href="paysitelink.com"><img src="urlofbanner.gif"></a>
and so on, plus you have to match the ad code you added to the paysite.
With Arylia its done a different way, you add sponsor, then the paysites, and banners, you can upload a banner, use a flash file, us text, or html.
I have been running Gallery Daemon for almost a year, but recently switched to Arylia version 3 (I use to run v2)
In that said, both scripts are nice, but Arylia does have advantages over GD.
I do look forward to the updates GD will have in 2009