Choosing the right flavor is tough, and taste reviews, especially for tobbaco-y flavors, are often not helpful. I personally couldn't stand RY4, though many people love it - it tasted like burnt sugary something to me. 555 seemed sweet and nutty, but I wasn't crazy about it. RY2 I have never tried, but from a couple descriptions I've read, it sounds a bit like 555. Early on, I wasn't thrilled with any tobacco flavors, as even if they tasted OK, they reminded me more of an unlit cig, which I didn't find particularly satisfying. I found that I liked coffee flavors, some of which had the kind of "dirty" bite of an analog. One day I tried a sample of menthol, and was amazed at how refreshing and satisfying it was - I had never liked menthol cigs at all. I tried a few different menthol flavors and eventually settled on Halo Menthol Ice, and it has been my daily go-to flavor for almost a year now. Get a bunch of small samples, or even try mixing your own (see the DIY e-liquid section of the forum).
Best of luck to you - hope you find the flavor that makes you say good-bye to cigs!