If you're looking for a WTFast alternative, ExitLag is a good choice. It optimizes routes to game servers in real time to eliminate lag, ping, packet loss and jitter problems. With features like a Dynamic Stabilizer, Traffic Shaper and Multi-Internet support, it's designed to ensure a stable and fast connection. It supports more than 1,900 games and apps, and you can try it with a free 3-day trial. Several pricing tiers are available to suit different needs.
Another contender is Photon Engine. This service is geared for cross-platform multiplayer game development, with features like advanced state synchronization and deterministic performance on Android, iOS, Unity 3D and Unreal Engine. It also offers voice and chat support, real-time matchmaking and cloud hosting with low-latency servers, so it's good for game developers of any size.
If you're looking for a more complete toolset, Azure PlayFab is a full LiveOps back-end platform for building and running live games. It includes multiplayer services, analytics, party networking, matchmaking and real-time data and analytics. Its pricing is flexible, starting with a free account and moving to a pay-as-you-go approach, so it should be adaptable to your game development needs.