Hi - Have you asked your doctor exactly why tamoxifen is a better choice for you? All of the current data points conclusively to an aromatase inhibitor (e.g., Arimidex) showing more protection against a recurrence. Unless your doctor is super worried about osteoporosis — because that IS the downside of AIs — I can't imagine why tamoxifen is the recommendation for you.
Admittedly, all the data isn't in on AIs yet, as it is on tamoxifen; they're still very new, only about 10 years old, while tamoxifen has a 30+ year history. Both have their plusses and minuses as far as side effects go, but an AI will give you better protection against a recurrence - for longer than 5 years, since you generally take an AI for longer than 5 years.
Newest data seems to indicate that an AI for 2 years, followed by tamoxifen for 3, gives the same protection as 5 years of an AI. So you might compromise with your doctor, and suggest this regimen... Good luck - PJH