Late reply but I'm an Avis President's Club member so I figured I'd chime in.

1. Car choices in airports are decent. When they see (or you tell them that) you are President's Club, the agents are usually willing to put you in whatever you want when I book Intermediate or Full Size. This excludes luxury cars. I have never been able to get upgraded into a Mercedes, BMW, Porsche, Tesla, Escalade, etc. I've tried for any of the luxury cars/brands I listed but the agents hold firm - they're unable to do it. I've maxed out at a GMC Yukon XL (pretty sure I had rented a mini van that trip), or a Lexus NX or RX when renting intermediate.
2. Car choices and upgrades at non-airport locations are garbage/non-existent. I've also found that these cars are not very clean, in my experience. I've stopped renting at non-airport and switched to Enterprise for my off-airport rentals because the Avis experience was so disappointing and completely devoid of upgrades. PC entitles you to a 2-class upgrade - apparently this does not apply to non-airport locations. Pretty annoying.
3. Pretty easy via the app but you have to redeem when booking. You can't decide to apply points while on a reservation or after the fact when checking the car back in.

Biggest gripes with Avis are:
1. The complete disconnect between phone support/customer service and the rental locations. If you want to confirm availability, or upgrades, or you have a dispute with the rental location - good luck getting through to them.
2. Their IT is garbage. App is the worst of the major rental car companies, as is the website.
3. Points earning is not good. I've rented probably 50 times from Avis and I only have enough points for like 7 days of free rentals - if that.

Just status matched to National Emerald Executive Elite and am looking forward to giving them a go. Avis agents at airport locations are accommodating of PCs, but that's about it. The rest of the experience is pretty bad.