For the past five years, for day use, it's been Estee Lauder More Than Mascara. It's not waterproof and my lashes never break off. It doesn't make my lashes uber-thick or uber-long, it's just a great basic mascara.
I like the new Maybelline Define a lash. It doesn't clump and defines well. If i want more oomph though, i do prefer chanel Inimitable multi dimensional mascara.