I would first determine where I could practice and what calibers were allowed. There are few firing ranges in many cities and those are indoor. Typically, indoor ranges frown upon firing shotguns (and some will also not permit rifles). Outdoor ranges may be a bit more flexible. I would also consider whether I was the sole user or others such as older children, spouses, significant others, etc. would be employing it as well. Living in apartments or condos with thin walls also may affect which firearm you choose because of the potential to shoot through walls harming others.
Firing a pump action shotgun takes acclimation and practice--it is a fine defensive weapon but slow to reload outside of its magazine. Rifles, depending on the caliber, often will have less recoil and perhaps larger magazines. Operating something like a lever action, pump action, or semi-auto, takes some practice as well. Depending on your jurisdiction, M1 Carbines and SKS's are fine defensive weapons. The M1 uses magazines while the SKS's generally use stripper clips to fill a fixed magazine. Some jurisdictions alllow the Mini-14 series which is also good. A M1 Garand is an excellent battle rifle firing a very potent cartridge but as a home defense weapons has some drawbacks, namely recoil, blast, big and heavy, and overpenetration if you live in a crowded area. You may also not be able to find an indoor range that allows you to fire .30-06 or .308 rounds. Pistol caliber firearms such as the late PC 9 and 40 by Ruger, Keltec subs, Hi-Point carbines such as their 9mm and 45 ACP, Marlin's 9mm carbine, pistol caliber lever actions, etc. are also pretty good self defense weapons and may be able to share ammo with a handgun which could be an advantage under California's new ammo rules. They are also light, light recoiling, available in semi-automatic, and reduce the risk of overpenetration in urban areas.
Good luck. John Farnam has a pretty good writeup in his book on shooting rifles and shotguns with a considered approach to either of them if you want a noted firearm's trainer's perspective.