Internet explorer is fast and smooth , though it does not support downloading at moment , it will be supported in upcoming update for all windows phone 8-> 8.1, it will support both download and upload. By the time you can use uc browser.
I have the #3 and on some websites embed YouTube videos doesn't work, says update flash or whatever. But I still use UC Browser. The major plus, it has Back/Forward buttons. For the listed two problems I use IE)