I used to run NOD32 as it was known as the lightest on resource usage, while being at the top of the pack on detection rates. They've remained solid over the years, but last time my subscription ran out they didn't run any sale for months, and I won't pay more than $10 - $20 for an AV program (I always caught NOD32 on a sale for like $10 on Newegg so continued to buy it).
I run MSSE now.