Hello!
1) Not a lot of pin out so it's easy to solder and desolder.
As for soldering, it doesn't depend on the number of pins. Once you have aligned
2 opposite corners, the rest will be fine.
As for desoldering, it depends whether you want to reuse the chip after desoldering.
But usually you don't desolder a chip unless it's already fried.
What I use is a hot air blower (the stuff that looks like a hair dryer, but that fries
you bald if you confuse). With this method, you can desolder quite large chips.
I have never experienced very large chips like old 200 pins FPGAs, but for 144 pin
LQFP or QFN it works fine.
2) One that is going to be around for a long time, popular one that have good support.
To my knowledge, this is the case of all MCUs. Any silicon maker invests a lot of money in
a chip development. Therefore he has to sell it for a long time, and in most of the cases,
you can still purchase them for decades. For example, you can still buy a Z80, which was
quite popular in the early 80s. You can also buy a 6811.
Dora.