It depends on your needs and how many of the people that you want to communicate with as using that platform.
WeChat may be the best for some, but if you have NO FRIENDS or family on it then this is not the best. Either, check with your friends and family what they are using (I'm guessing you're meaning in Zimbabwe) and join that network/application.
If not, then try and join one that meets your needs (whether you want to do voice calls, send instant messages, or save on data), then get your friends and family to join that network/app as well. Good luck with that though.
Currently, WhatsApp has the greatest (If you don't count Facebook) uptake here in Zimbabwe and it'll be easier for you to join this network.