PhD Decision Questions-UT or UMD-CP

[monday_tree]

Hello,

I have been admitted to the Microbiology Department at the University of Texas at Austin and also the Cell Biology and Molecular Genetics Department at the University of Maryland at College Park.

I need to make a decision between them by the 15th and I'm finding that a little hard.
Austin is offering me slightly more money and have also waived the TA/RA duties for the first year, but maryland seems to have a better research fit.At maryland I will have to undertake TA duties.
I am interested in Virology and Microbial pathogenesis.

Does anyone know about these two programs in these two universities? Anything that might help me with my decision?
Is doing TA duties in the first year really that tough?

My other questions are rather general.
First, since I need to take a decision by the 15th, how late can i respond( ie. late 15th, early 15th, late 14th)

Do I call them or e-mail them? Whats the usual procedure?

And once I have comitted to a particular University, how binding is it? :o