When is it smarter to get a root canal or to get the tooth pulled instead?

Non-restorable: If a tooth is decayed or damaged to the point that it is not restorable with a functional crown that has a high level prognosis for many years, then other options probably need to be looked at. If the tooth must be extracted, usually the best way of replacing the tooth would be with an implant. There are various criteria that must be met for this, but your dentist or specialist can advise you.

Save 2th if possible: If the tooth is salvageable, that should take precedence over extraction. See multiple specialists to get different opinion. An microscope using endodontist, periodontist and your general dentist should be involved in the decision. I would do everything to save my tooth.

Depends: If you are relatively young (14-18) and you have a well formed third molar behind the second molar, sometimes it might be better to remove the second molar instead of saving it with root canal treatment.

Saving teeth: It is always smart to save a tooth that is restorable and has a good long term prognosis even if you get a root canal treatment. Make sure you discuss all the options and ask for the long term prognosis of the tooth in question to make an informed decision.

The smartest: Thing to do is to discuss your options with your local, treating dentist. Which tooth is it? What condition are your other teeth in? What's your long term plan? If you extract the tooth, it should be replaced, which will cost even more. Treatment planning requires more than just posting a question... Please make an appointment with a local dentist.

RCT or EXT?: If the tooth can be salvaged with root canal therapy, restored and maintained for a long time, it would be better to save it with rct. If you will not properly take care of it, it is too far decayed, has severe bone loss and mobility or has a poor long term prognosis, it would be better to extract it. Your own dentist can properly evaluate it and guide you into making the right decision what to do.