I think I'd go with the romisen, they are quite respected as far as budget brands go. However, tank has a pretty good reputation too. The romisen has a newer led though.
I personally don't trust ultrafires, hear too many bad things about them.
I'm a newbie to all this but i did some research and bought the romisen rc-d6. I work in a sawmill and its great to stick it to some steel (very powerful magnet) in a dark space to work on something. Everyone there uses the 2aa maglights and comparatively this little light is several times brighter! It's also my second romisen light and the build quality and feel seems much better than the other budget brands (dare i say almost fenix-like?) I strongly recommend this one if it suits you.
If you've gotta go cheap, go iTP EOS... I got sick of Chinese lights being unreliable (with a few exceptions). I used to be a "Buy a cheap Chinese light to mod" guy... now I fool around with P60 drop in stuff... You will one day too!!!! Muahahahaa