If you will use 5G network, the 10a seem to have better power usage.
5G is particularly power hungry prior to the improved cellular radio in 9th/10th gen Pixels with the exception of the Pixel 9a. Either way, setting the cellular mode to 4G (meaning 4G and below) or the GrapheneOS 4G-only mode can save a lot of power.
When considering the duration of support, it is necessary to take into account that Google restricts the battery of the A series before the device is four years old. It is more difficult for those on alternative OS to benefit from their battery repayment/replacement campaign.