Why? Because more than one choice dilutes focus -- on both ends. It more than doubles the amount of time spent on marketing (different rules for setup and presentation), and paradoxically makes customers less willing to buy. Two very similar choices may not be terrible, but 4 or 5 will actually lose customers. I used to be an insurance agent, and I was taught this in my training -- and I did, indeed, find it to be true.
As for which, I don't think it matters much, since sales are most likely to come via the Lua site links. I would just pick whichever is either the easiest to deal with, or has the been margins, and focus on that.
Having more variety of merchandise may seem to contradict the 1st paragraph, but the key is different (and possibly complementary) choices, not similar. For instance, you might have two distinctly different coffee mugs, two different T-shirts, two different pens, etc. And your customer might buy each of them. What you *don't* want is 35 different coffee mugs, 100 different T-shirts, etc. because the potential customer will simply lose interest after looking at a couple of them and go on to something else.
These are actually fairly well-known principles (among professional salespeople, anyway), but seem to be counter-intuitive to techies. The techies wants lots of choices, and the sales professional just wants to make a sale and get on to the next customer.
