I buy boat loads of batiks and love everything about the stuff!! My local shops carry lots and lots of it so I have never purchased batiks online. The color is so very important that I think I would probably always want to see it in person before buying. I usually unwind the bolt a couple flips to get a fuller view of the variations in color, pattern, etc. Unlike printed cottons, batiks will always vary by bolt so what you buy online may look very different from the same line you saw in person. That is their beauty, for me, the uniqueness of each piece.
As for choices of colors, it depends on my mood at the time of purchase (I buy for stash, not project). I love the brights and lights and now they are even making some that are reminiscent of colonial colors. Yum! I also like the earth tones, deep colors, all colors I guess. What I don't like, and this is just me personally, is the muddy looking colors, not muted, but muddy and I tend to stay away from bolts with non-analogous colors on them.
Something to consider would be having a difference in value, color wise. For example, I have a lot of red batiks, but they are all the same value. It limits what I can do with them together. It's as if batiks have to blend horizontally (across the color wheel) instead of vertically (by depth of value of the same color). See what I mean? Try to add some depth as well as width to the selection you offer, no matter what colors you select.
My local shops each carry different styles, to reflect the owner's tastes I suppose. They have not tried to cover all bases, and are doing very well with that philosophy. It means I go to one for reds, blues, purples and greens, and the other for yellows, oranges, creams, and browns. Everyone benefits!!