Agree with @Afraser everyone can react differently so you really just have to start with one and see what happens. I started Letrozole almost 3 months ago. Since starting i have gained a couple of kilos and I get pain in my hands at night. A few stretches in the morning to get my hands going and I am ok.
I see my oncologist later this month and will discuss these side effects but expect to stay on Letrozole and be monitored. I was on tamoxifen for 20 months until side effects got unmanageable and then switched to Letrozole. It's been an improvement from the tamoxifen for me. Just try and monitor and report any side effects to your oncologist. Good luck