Well this depends on the cryptocurrency exchange platform you use. For example binance launched a new features yesterday allowing Nigerians to buy naira on the platform using pair to pair P2P. I’ve tried it and it’s fast and effective. Quidax just launched their own P2P feature today. Check those two platforms
I think the fees also matters. Some trading platforms charge a lots of fees whereas some of them do not charge any fees at all. However, you may need to pay a small fees when you withdraw from your trading account or main account to your personal wallet.