The main differences between Roam research and Obsidian :

1- Roam research has his own proprietary file system and only works online (which means your notes lives on their servers – and need to be connected to the internet to take notes), while Obsidian uses only markdown (text) files.

2- Roam is structured as an outliner, while Obsidian as a text editor.

3- Obsidian is free, roam isn't.

4- Roam is slow, Obsidian is fast.

So the best thing is to see whatever floats your boat!