It depends on what you want to do next. If your plan is going to a major in the US then probably a regional is a good way to go. If you're planning for an airline like Emirates, Virgin Atlantic, or anything like that then 737 time might be helpful. The only problem is that COPA has a pretty long upgrade time from what I know, so if then you're plan is to go overseas in some airline like the ones I mentioned you might be missing the TPIC time.