I just got a Samsung A71 and I know I’m going to drop it at some point. What case be most likely to prevent damage? Any brands/models known for protecting well?
I’ve used OtterBox cases on several phones.
Seconding Otterbox. That’s the gold standard of phone cases, IMHO.
I’ve used LifeProof for my last several phones.
Otter box. I use Defender model of theirs. Have on the last several iPhones of mine. Their Commuter model is also good if you wish a slightly slimmer design-several of my children have had good luck with that model. I need the Defender cause I am really hard on phones!
Amazon is the cheapest source for Otterbox I’ve found-much less than other stores/sites.
Consider a tempered glass screen cover too. Best $20 I ever spent on phone screen protection-even against drops. The Otterboxes come with a plastic screen cover-I always push that out-it is murky and interferes with capacitive touch I think.
This https://www.amazon.ca/gp/product/B087JJJMJT/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 is in the mail and should arrive in 2 days.
Are Defender and Commuter the only two options?
No, they have others. Depends on the level of protection and the silhouette that works for you (and your phone handling adroitness) My phones live a hard life 
Lifeproof is the next brand that my IT specialist son recommends BTW. Then Zagg and UAG.
The Amazon screen protector is exactly what I meant. 
Boo
I see that the Defender isn’t compatible with third-party screen protectors. Does it have its own?
I can’t seem to find a Defender for the A71.
Opinions on this one? https://www.amazon.ca/dp/B085T8Q34N/?coliid=I1QMGHCTGL5VQY&colid=2VAW6GHURYDY0&psc=1&ref_=lv_ov_lig_dp_it
With my Defender it came with a built in thin plastic screen protector. That’s the one I just pushed/pulled out manually and went with a tempered glass one, then put the Defender on top. As I remember, the plastic screen cover is just lightly glued in.
It may well be that the Commuter doesn’t come to fit your phone, The Commuter model might. Or a Lifeproof, Zagg or UAG, they do more Android versions.
From my tip-toeing around for those brands on Amazon, it seems that none can be shipped to your area. Don’t know what to suggest there. Some market share control thing?
I’m using the Canadian Amazon. The one I linked to can be shipped to my area but perhaps not to yours.
See, you knew more than I did 
Since I couldn’t get the Defender for the A71, I hesitated between these two https://www.amazon.ca/gp/product/B07ZWJ9XXF/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1 https://www.amazon.ca/dp/B085T8Q34N/?coliid=I1QMGHCTGL5VQY&colid=2VAW6GHURYDY0&psc=1&ref_=lv_ov_lig_dp_it
One is rated 4.7 and the other 4.8. They’re both Amazon’s Choice. In the end, I ended up going with the one that reminded more of Batman, the Spigen Liquid Air.
I have an iPhone and for the last few years I’ve been using the wallet type case. I love it! I don’t even have to use a screen protector because the screen is always covered when not it use. (The top is padded.) I like being able to put a few dollars, my ID and my debit card in there and not have to always have my purse (or for a guy, a wallet) with me.
I got two sets of protective screen/camera protectors and wondered why. After having messed up twice, I can see why they’d include extra sets.
A couple of phones ago, I tried to put a screen protector on the glass but didn’t do a good job. So I went to one of those phone accessory kiosks in a mall, and the guy there did a much better job of attaching the screen protector than I did.
Spigen generally makes the best cases, IMO. Second to the OEM cases (I have a Google fabric case on my Pixel 4XL right now), but a good deal cheaper.
That’s a good idea. Attaching a screen protector is one of those things where once you have some experience, it’s easy. But when you don’t, it’s an exercise in frustration.