Deca is often taken with winstrol, as winstrol competes for the progesterone site and can help prevent progesterone gyno. Arimidex won't do a thing for you on a deca-only cycle. Arimidex prevents aromatization (conversion of testosterone to estrogen) so it only works for aromatizing steroids such as testosterone to reduce the chances of getting estrogen gyno.
Personally, I would do testosterone with deca because it works better and I enjoy having a healthy libido throughout my cycle. A common cycle would be 8 weeks of Test at 500mg/week, Deca at 400mg/week and optionally add winstrol at 50mg eod or ed the last 5 weeks of the cycle, with arimidex at .5mg ed through the entire cycle, tapering off during pct.