A fairly boring topic, I admit, but also a very important one for me.
I wear leggings quite often. Not generally in public, but all evenings spent at home, most weekends outside of summer, and while I'm sleeping, I've got leggings on. That's a lot of time spent in stretchy black pants, and that routine suits me very well.
So now, at 6 months pregnant, I've experimented with a couple versions of maternity legging. One I would call higher-end, the other middle-of-the-road to low, and the last the low-low end.
First are the pair pictured above by Blanqi. These are quite nice, but for me almost too much. There's a lot of thick fabric here, and the material is listed as 'breathable' but I'm not entirely convinced. I've gotten a bit sweaty in these a couple times and I wasn't necessarily feeling that moisture-wicking they mention on the site, and they're much too warm for me to sleep in.
I will say, in the plus column, I do like the coverage they offer if I do go out in public in them. I like having one pair of these to run to the grocery store or travel in.
My last issue with the Blanqi leggings is the 'support' factor. I don't know if I'm just not big enough yet to appreciate that these are more supportive... but so far I'm really not getting any support from these at all. I will do a short post again in the future if I find otherwise.
Next on the price scale, are the Gap full panel maternity leggings (here). These are my favorite of the three. Comfy, stretchy, long, breathable and probably a skosh see-through. That's my only complaint, otherwise these are working really well for me.
Lastly are Old Navy's version (here). I just don't really like them. They're thin, they're not very long (I'm 5' 5" and they barely come up bast my navel), they're not as soft as the Gap version and they just don't really compare to either of the above. If you're on a budget and you just need some cheap leggings, these will serve their purpose, but I personally would just wait a few days for a sale at Gap and get those at 30 or 40 percent off.
I will say, however, that I only just noticed that Old Navy also offers a 'heavy knit' version of their leggings, so maybe those are worth a try. (Though try for a sale day, both Old Navy and Gap run 30% off sales quite often).
Best of luck if you're trying to figure out maternity clothes in general, I have found it to be a chore, but so far the Gap and Old Navy have served me well.