All torrent clients follow the same protocol. Therefore, properly configured, all torrent clients upload and download at the same speed. Some clients are harder to configure than others, and this may result in error messages.
Azureus is like MS Word. It is extremely powerful, with masses of configuration options, and the ability to plug-in even more. It is coded in Java to allow it to run on multiple operating systems, but at the cost of requiring the Java Virtual Machine to be running to support it.
Try uTorrent. It is like Notepad. It has all the essential functions but no more. It is extremely tightly coded, specifically for Windows, so it uses the least amount of RAM possible.
So, go for uTorrent.