Alamy's unpredictable (for me), so some months it's much more than 123rf but other's Alamy is zero and 123rf has never been zero. Taken annually, 123rf has always easily beaten Alamy.

As far as which sites to place your work with: it's complicated.

There are some disreputable sites that just shouldn't get your work (you can see the discussions here about sites which have been caught in all sorts of underhanded behavior). For other sites with a sales track record, my view is that it's unlikely, for most of us, designers who shop at a particular site or two will go and hunt out your work if it's not there. You probably will not see those sales as the designer will buy someone else's work from their preferred sites.

When sites are new or trying to grow, it's absolutely worthwhile to withhold providing work to a site that has terrible prices or policies, but once it's established, unless you can organize a mass exodus, I don't think you'll change where designers buy.

I've left a number of sites over concerns about their practices or terms, but not over low prices per se.