You must have found Android by googling - I've rarely seen it ever mentioned in the NZB community. I used Android years ago. As I recall, back then it was one of the first binary newsclients to natively support SSL connections. (Otherwise, you needed an add-on like Stunnel to connect to SSL servers) Although still perfectly usable as an NZB downloader, Android has become a little outdated now, since it lacks some of the more modern automated features like auto-rar/auto-par and backup-server support. At least it's free (nagware)
regarding speed: All binary newsreaders will download at the same speed (and will max out your ISP connection speed) if set up correctly. On many newsreaders, the default setting is often only one connection/stream/thread. I bet that's why Android is slow for you. To get maximum download speed, you need to increase this number to at least 3 to 5 streams - or possibly more (Astraweb allows up to 20 streams)
As far as choosing binary news clients goes, lot depends on how you use Usenet, how advanced of a newsgroup user you are, what features you want, and how well you learn new things. (software with the most options, setting choices and features will naturally have the longest learning curve) Would you prefer software that's simple to use or a client packed with lots of features?
The Usenext newsreader can be considered a sort of all-in-one client, since unlike many binary grabbers it has a thumbnail image viewer and media player integrated (instead of having to install a separate piece of software) but everything that Usenext does -and a lot more- can be found in other software apps and online websites.
Some popular binary clients are Newsleecher, Newsbin, Altbinz, Grabit, and SabNZBd. There is also NZBPlayer (and its many clones) for streaming video from usenet.
Have you read this recent discussion thread about news clients?
http://filesharingtalk.com/vb3/f-newsgroups-79/t-news-readers-352679