Answer to your question depends on your current needs. If you go for the best quality choose AVI. If you want lower file size and better performance get MP4.
AVI is better quality in my opinion, and i love to use it. it just sucks cause AVI usually creates larger files. which can cause bad playback in certain video editing software. it seems that MP4 (NVIDIA NVENC) is the one i have been currently recording with. there is some lack of quality, although its not that bad. but playback is smoother during editing.