There's a lot of strains that are in the THC percentage range you mentioned, but don't think potency actually equates to THC percentage, at least not totally. It comes from having a better or proper ratio of cannabinoids and terpenoids but than THC percentage alone.
An example is real true Durban Poison. It is not rated high in THC, but it can knock you upside your head. I had friends who smoked what I grew and thought it had to be in the mid 20% range, but it's not.
The first thing though is do you even know what you like, as in a pure landrace sativa, a 100% sativa hybrid, a sativa dominant sativa/indica hybrid, a more or less 50/50 sativa indica hybrid, an indica dominant sativa/indica hybrid, a 100% indica hybrid or a pure landrace indica?
Which do you like the most?
If you do not know what you like and are a beginner grower and smoker I would suggest Sensi Seeds Skunk #1. There isn't an easier strain to grow, it produces very well, if you will be buying feminized seeds right now they're like $31.and change for 5-seeds at Attitude, which is as cheap or cheaper than the pure garbage you get from places like Green House Seeds and Nirvana for the same kind of price, it's one of the most famous strains ever, it won the very first Cannabis Cup in 1985 and has been used in as many, or more, crosses that has since followed, it has a fairly short flowering period, and it wasn't used because it is crap, but potency-wise it would now rank in the med-high range. So you don't sit down and try to smoke an ounce, you do one or two hits and wait and see if you want more.
For the price, and coming from a quality breeder rather than some talentless pollen chucker, it's a great value for the price for anyone, and in particular a new grower who wants quality but is not ready to shell out around $100.00, give or take a little, for beans until they got their sea legs under them when it comes to growing.