Having tried for several 'chievos, Stellaris has the easiest by miles, rng or not, play several games in smallest galaxy and you'll get them, there's enough replayabiility to make runs interesting
HoI4 ones are usually tedious, but that might be more the flaw of the game, which becomes tedious soon and is very inflexible in approach
EU4 feels like every other one needs you to do WC or close to it, and WCs here are tedious too (for me), but you have good variety of options, there's more than a single way to advance unlike HoI4
CK2, I don't know, feels like you need some luck with RNG and good knowledge of game mechanics, they are the least appealing to me of them all