If you are absolutely certain you don't want another baby down the tract I would have the tubal ligation. If you were having a vaginal birth then I would probably say mirena but as with the C/S they are already there then thats why I would say tubal ligation.
Tubal ligations are reversable although not as successful as a reverse vasectomy. The only people I have heard complain about side effects of the tubal ligation is on the bb forum. There are many many people who have absoluteley no side effects from the tubal ligation. The mirena is also a good option however you do need to check it and you do need to continue to be worried about your contreception until your in your 50's and you can be sure menopause is complete if you don't want to risk getting pregnant again down the tract.
In saying all this you sound very undescided and it doesn't leave much time to make the choice to have a tubal ligation with your C/S. I wouldn't rush into any descisions you may regret down the tract and at least with the mirena its easy to remove where are undoing a tubal ligation takes hours under a general anethetic, a hospital stay and no guarantees it will be successful at rejoining the tubes once the clips are removed. Congrats on your bub how exciting that you will meet her/him so soon.