Consular vs COS with 3 years OPT Remaining

I got my H1B picked on my first attempt before graduating, I’m confused between Consular Processing and COS. Given I have 3 years of OPT remaining is consular processing the ideal option? I know I’ll save money on taxes. What are the downsides in choosing Consular Processing apart from not being able to transfer my H1B before I start it?