I've been a web and UX designer for about ten years. I've mostly given up client work, but I stay fresh through research and occasional practice. As a writer for Web Designer Depot, I spend a lot of time researching the tools of the trade. So far, my favorite app for wireframes has probably been Google Draw. I'm not even joking. Between the drawing features, the available shapes, and the collaboration and sharing features, it usually does what I need. The one caveat is that it can only do low-fi wireframes and prototypes. If you need to do a lot of prototyping in mid-to-high-fidelity, you'll want software dedicated to that. The point is, choose the tool that helps you get YOUR point across to YOUR client, as efficiently as possible. Are you developing interfaces for smaller, simpler sites? Google Draw can do that. Do you need something more complex? Look into Adobe XD, or InVision. I... actually wrote a massive guide on this subject, but I don't know what the policy on links is around here. I'll just say this: tell us what you need to prototype, and for whom, and we can give you more targeted suggestions.