Root canal/crown or remove teeth?

If there is enough tooth substance RCT/Crown is better.

If you're not having any toothache or sensitivity, then you may not even need root canal treatment. The best approach is to remove the old fillings, remove any decay using a caries detecting dye to show up the caries, then seal up the cavity with a material suitable to take a crown. (Assuming the caries has not gone down to the nerve). Wait a month or two. If the teeth are still OK, then go ahead and get the crowns.
It's always better to keep your natural teeth as LONG as possible. Artificial teeth such as bridges and implants have another bunch of potential problems !