Megaupload because it's ridiculously fast even for non-members.
All other sites are limited to around 100~300 KB/sec, while i can get up to over 6 MB/sec using Mega.
Time Limit - I assume you mean the wait time. I don't really care as long as the download speed makes up for it.
Number of Downloads Limit - I can bypass this with dynamic IP.
File Size - What? Most everything I download is split up into 100MB parts anyways.
Speed Limit - This matters the most to me.
Completion of Offers - I would not download from a site that makes you do this.
Inability to download multiple files at once - Don't really care, speed limit matters more.
CAPTCHA - Don't really care, I can do these easily.