After due consideration I ______ to accept your offer.
A. decided
B. have decided
就本句本身提供的语境(尤其是其中的your)来看,最好(但不是绝对)用现在完成时:
After due consideration I have decided to accept your offer. 经过慎重的考虑,我决定接受你的建议。
如果将句中的 your 改为 his, her 等,则AB均可(自己体会):
After due consideration I (have) decided to accept his offer. 经过慎重的考虑,我决定接受他的建议。