Unless its a RHD actual coupe, please refrain from calling it a coupe... It's not. It's a 2 door sedan. Also, I'm not quite sure you're even ready for a swap if you have to ask which is "better." if you had the knowledge required would you know which engine would fit, which would give you power/reliability you want, and which is in your budget?
It just feels like you're not ready with the requisite knowledge to begin something as involved as a swap; especially something like an SR or rotary where neither were designed for a 510.