For me, in this order:
1. financial (even better if it's a niche, like penny stocks)
2. security electronics, like alarms, security cams, etc.
3. health, especially health supplements, dieting niches, etc.
4. home niches, especially specific kitchen items (kitchen islands, kitchen counters etc etc, or specific bathroom items)
5. jewelry, then clothing & fashion
6. novelties and everything else pretty much flattens out in ctr. There are spikes and lows in all kinds of other niches of course, but the above is my general ctr hierarchy across about 250 minisites I have/had with myself and 2 minisite partners. Note that I don't have 'every' kind of minisite so I can't give a balanced list; for example, I have no law-related sites, only 2 automotive niche sites, no travel sites, etc.
*In addition to that order of ctr hierarchy, that is also pretty much the order of highest-to-lowest CPC too, at least in my sites.
