D.N.
I use Maybelline, one is Colossal and the other is Full and Soft. I have found that the first use or 2 of most tubes of mascara does tend to clump so I use a napkin--less lint than toilet paper--to blot the brush a bit. After a couple of uses, it is usually fine. A friend swears by Loreal but I found it to be clumpy.
Also, if you wear more than one coat, go very light the second time and only do the tips.