For bellows.
Leaving your upload as unlimited vs. throttling probably depends on the combination of your bit torrent client, system, network connection, and the network between you and the others in the swarm. Best advice I can give is to test out different settings and find what works for you.
I used to keep my upload capped at a really small level (~6kB/s). From what I understand about the BT protocol, if you up to other peers they are more likely to send stuff to you. So I tried increasing my cap and I found that it increased my average download rate until I hit 65-70 kB/s Up. Once I hit that point my DL started dropping and web browsing slowed to a crawl (suggesting that either my system was slowing down dealing with uploads or my net connection was hitting it's max -- more likely the latter). So I set my cap at 60 and it's been getting good DL speeds ever since.