Asked on Reddit: Which of Rust, D, Go, Nim, and Crystal is the strongest and why?

[jmh530 via Digitalmars-d]

I'm not really familiar with Go, Nim, or Crystal, but I spent 
some time learning about Rust yesterday. I thought it was pretty 
interesting. In particular,
1) The GC is optional (memory safety is enforced by the type 
system and #2).
2) Smart pointers with separate operators and support for 
reference counting.
3) Immutability by default. Someone (somewhere) made an 
interesting point that it can be conceptually convenient to have 
the most restrictive choice as the default. I'm not sure I agree 
with that (maybe the most common choice used in good code), but 
at least immutability by default it can be helpful for concurrent 
programming.

All of the above seems to have a downside too
1) The memory safety stuff is pretty confusing. Move and copy 
both use the equality operator, but you're not always able to use 
it depending on the type. I think a separate move operator would 
clear up some of the confusion. I also didn't really get a good 
handle on how borrowing and lifetimes worked, but it seemed in 
need of a simpler explanation.
2) The plethora of options for smart pointers and reference 
counting
2) No prefix operators like ++a. Perhaps a consequence of 
immutability.