Trying both is a good idea - people differ in their responses.
Letro's potency is sometimes overstated, though it is stronger mg. for mg. than arimidex.
In men, letro at 2.5mg per day cuts estradiol by about 2/3 vs. 1/3 for arimidex. There was recently a thread about this, citing some studies.
A dose like 0.25mg per day of letro is very reasonable. I'm taking that now (against test-e and masteron) and doing well - libido, no joint problems, all good. I prefer letro or aromasin to arimidex, but have no big issues w arimidex.