They're not "better", they're different. Definitely do that and get a few of each. Ideally, I'd like to have all
three around. I've had all three at once and would reach for each for different things.
510 - Good all-round performance, probably the best vapor/throat hit and the least flavor.
901 - Outstanding flavor, especially sweet flavors - I love these with fruit flavors.
306 - The best balance between the two and if I had to have only one, I'd probably pick one of these.
There are exceptions in each category, but overall, with everything else being the same, that's how I see them. For example, SmartVapes 510 dripping atties have much better flavor than others I've used (I prefer their 306's). I've also used LR 901's that completely washed out
juice flavor without dropping the voltage down to 3.3v. While I love 306's for dripping, the sleeves stink (start tight but quickly loosen too much and actually come off just sticking to your lips, or else they crack). If you drip on a 901, get an o-ring to put around it, and situate it just below the vent hole on the side - it really helps with leaking (or else grab a drip shield if you find you like them).
Don't forget an adapter for the 901 of course.