Valtrex is more convenient - usually a once a day dose - and though a generic is available now, it is generally more expensive then acyclovir
is inexpensive, but is a twice a day dose. For some, convenience is more important, and for others, cost is. No right or wrong answer - up to you.
Also make sure that you don't have another infection, like yeast or bacterial vaginosis, that is causing you to have more outbreaks. Secondary infections can wreak havoc on herpes.