Because this will be different with everyone, I will tell you what I have been doing.
I smoke about 6 to 10 times a day (6 to 10 cigs worth) and I add a drop or two to my cartridge about every fourth time instead of waiting for it to dry out. I don't know if it makes a difference or not, but my theory is, keeping the atomizer wet seems like a good idea. Smoking as I do, my battery lasts about two days.
I have no idea on the "best" juice! I guess it depends on what you like. I scale "the best" on the basis of whether or not I can tell what the flavour is easily and whether it does in fact taste like what is says it does. Also on how strong the flavor is.Taste is so personal. I have noticed some people saying the like a good throat hit. Personally I like when it is smooth, but I want a lot of flavour.
I have only tried the stuff from puresmoker, Crown7(carts only), and Johnson Creek. I won't even go into Crown7 since they don't sell juice anyway. Personally, I have not been impressed with Johnson Creek. My roomy got a sample pack, which included all of the flavors they carry, and they just don't really have any flavour in my opinion. If you prefer your vapors flavouring to be very light though, you may like it. Over a span of four days I would randomly drag on her ecig to try whatever she had in it. I usually couldn't guess which flavour she had put in the ecig at all.
I have liked the three flavours I got from puresmoker. I could taste the flavours and had no question as to what the flavour was. Only you can judge what flavours your mouth will like though.
A lot of people here seem to like stuff from electroniccigarettesales.com (Jane, I think?!). I personally find the website obnoxious to navigate so haven't ordered from it. Goodluck. And please mention what you find that you do like, cause I too am plenty curious to try different stuff.