Generally I switch to use an accelerator when a download is coming in a bit slowly – for example in my browser, if something’s downloading at 40kb/sec and will take a long time, then I’ll test in a terminal to see if it will come faster and then cancel the browser download.

Silly test if you ask me – next time find something that’s slow and see if it speeds up! My connection will go to 700kb/sec, and I’ve seen 40kb/sec download today – with axel around 125 and with aria2c 150kb/sec. It arrived in around 2minutes on both. I’ll test with other downloads before selecting a favourite (currently I have them set with aliases for ‘get1′ and ‘get2′ to compare easily also with ‘wget’)

Sorry, but I think you comparison is a bit vague, because you do not compare features, you are only comparing platform fitness.
I don’t know how it is at the present moment but when I tried axel, it was unable to handle files bigger than 4GB. Pass that, It haves no cookies support nor https support. http login neither.
With aria2, for example, it is possible to download rapidshare files (with a premium account), either via –http-user/pass flag or via saved cookies; you can use a file to provide a highly configurable list of links (I mean, besides the link, you can provide in the file the md5 checksum so aria2 checks it automatically). To name only a few. OTOH, you are right, axel does a lot with so little code and it can use proxies too.

Of course, as you said, we have to choose the one with fits best. For me is aria2.

On topic I can do no more than echo what you’ve already stated. I actually don’t use either anymore because with or without them I always seem to end up with about a 1mb d/l speed. I dunno, I may just be lucky..