Framerate > resolution, all the way.
I'd take 720p/60fps over 1080p/30fps.
With 60fps you get that smooth, snappy sensation that just makes games feel better.
Having said that, 30fps isn't a dealbreaker; I certainly wouldn't want to play Splatoon or F-Zero GX at 30fps, but in slower paced games it's fine. Obviously 60fps would always be better, but sometimes that's not possible due to gameplay rather than just graphical considerations; Breath of the Wild for instance couldn't be 60fps even if it was 480p because of the demands of its physics-driven open world.