Grin will be outdated once LTC implements mimblewimble.
Beam will be outdated once LTC implements mimblewimble.
ADA is being developed by academics with not a lot of real world success and they're behind on any possible schedule, their business plan also has little value for real world businesses.
I'd invest in none of them.
Litecoin will implement mimblewimble? And if this will happen they will implement to the side chain not not mainchain, right? I am not a fan of this solution to create everything on next layer.