Eh idk its pretty personal and there's many I like for different reasons, I personally just prefer taste of energy drinks over most sodas. For Monster my go to are Monarch, Pacific Punch, Khaotic, Pipeline Punch, Nitro, Mango Loco etc | Ultra Rosa and Ultra Strawberry Dream likely my favorite sugarfree ones. Nowadays there's just so many options at least here in bigger stores.
For RedBull basic, blueberry, winter pear, summer ones are decent, coconut/blueberry decent etc.
Overall like I said Monster better for price and are bigger, but also sweeter and taste more "fake". RedBull more expensive for less but taste more premium and not as fake IMO.
Overall would just recommend basic RedBull its pretty safe and tastes like... well energy drink.