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Rising Star is fun and easy to get into. Here's my link. If you don't want to use it just remove the ? and bit after.

https://www.risingstargame.com?referrer=gillianpearce

What will be the initial investment in this game ?

I'm pretty sure it's free to play. It was when I started playing but that's a while a go but I think it still is. You can grind your way up.

Splinterlands is biggest and most complex so not the easiest place to start, in my opinion.

Yeah i have heard of it, it will take a lot of my time that i don't have at this point of life. So splinterlands is out of my list.

dCrops is a farming game and lies somewhere in between the other 2 I've mentioned.

There's also a new game called Go which I haven't tried but lots of people think highly of.