Grading for long term preservation?

I recently pulled the Mega Charizard X from Phantasmal Flames (125/094). I am not interested in selling it at this point considering how cool it is and how Charizard cards commonly rise in value. But, I am considering getting it graded for long term preservation. I’ve been debating between PSA and TAG, but do not know the best choice to make if I am not interested in selling immediately. I may sell it eventually, and wanna keep it in decent condition over time. Or am I better off not grading it at all and storing it another way? It is currently in a penny sleeve + toploader in a toploader binder Let me know what you think!