Great question that's asked a million times... I think it can be broken down into different categories.
You have Sativa, Indica, Sativa/Indica (mix) and Autoflowers, so you could pick your four out of these categories, or...
you could choose by region... Afghani, Thai, African, Hawaiian, Columbian, Jamacian, Mexican...
Then you have the sub-categories like Skunk, Kush, Purple, Cheese, Haze, etc...
Then you have specific qualities like yield (big bud), flower time (early girl), taste (sweet tooth)...
Or you could just pick from what is popular or classic... (white widow, AK-47, Northern Lights...)
or you can mix and match differing criteria.
I am personally growing Blueberry (always wanted to try it, hoping it tastes as great as it smells), White Widow (this seems to be the most popular strain so...), Cheese (with that name it has to have a great taste/smell), Super Lemon Haze (won the cannabis cup, wanted to try a sativa, plus I like lemon!)
Does anyone know which is the sweetest smoking strain? I want to smoke something that tastes like candy!