Cheap phone with latest Android version or top brand with older version

I would never buy a no name brand product. No support, no updates.
I wouldn't even buy the older phone.
Motorola makes a great up to date phone with a great battery and storage space, in the Moto G7 Power, or Play versions, under 200 dollars.
https://www.tomsguide.com/us/moto-g7-power,review-6340.html

 

I wouldn't get Android 6. Is it a high end Samsung like a Note or S series.
Which country are you in?
How much do you want to spend. Are performance, features or display important to you.

Motorola and Nokia, for example, have good / great new devices which will have 1 to 2 Android OS updates after Android 10 now or due, and 2 to three years of monthly security updates.

 

I missed some of your question. Apps will continue to work unless storage, display and performance limit some apps and app developers updates from continuing on your device. I had a Motorola on Android 7.0 until last week and it worked great. Security patches ended in 2017 or 2018.
You are heading into battery life problems unless removable replacements are available.
I was considering a used Moto G6S+ or new budget Nokia 5 3.

 

What kind of budget limit do you have? If you're trying to buy a cheap phone you have to lower your expectations and be aware of the necessary compromises.
-- If you buy a little-known brand phone you're taking a big risk it's a substandard phonethat will most likely have no tech support if you need it later. It will also be less likely to have any substantive online support.
-- If you buy an older, brand-name or pre-owned phone running an already unsupported version of Android, the phone itself may be fine but the operating system is dated and no longer receiving any security updates. At the very least be very wary of what you do online, and very, very judicious about what apps you install. Today's Internet is a really hazardous mess so you'll be using a device that has security and privacy issues.
-- Ebay is a great source for significant deals, but you do have to careful who you're buying stuff from. Smartphone deals are a big business for scammers so a lot of people think they're getting a bargain but end up with phone that's barely working, or blacklisted, or FRP locked. Be sure to buy only from reputable sellers.
-- You can get buy budget phones for under $300 that will have a warranty and are suitable for most consumer needs as a day-to-day phone:
https://thewirecutter.com/reviews/best-budget-android-phone/
The Moto G7 Play is under $200 with a respectable feature set:
https://www.digitaltrends.com/cell-phone-reviews/moto-g7-play-review/

 

Roll the dice...