Get both EADs but use OPT EAD. Are you going to be on STEM OPT or regular? If STEM, more the reason to use it as TPS EAD may or may not be extended beyond 2018.

Benefit of getting the TPS EAD even if you don't use it now, is that you can instantaneously change employers without any additional USCIS paperwork in case such a situation arises that you need to quit your first job.