"better than" is in the eye (or should I say throat) of the beholder. Both models are excellent and popular ... and are the two most common fittings for
mods. Neither is better made or more reliable (on average) than the other
and they are comparably priced. You can get a two battery, two atomizer 510 kit for as little as
$35 (and that is
Joye 510, not one of the clones). Most 901 kits (which may be a few dollars cheaper than many 510 kits) come with only
one atomizer.
The 510 is
wildly popular. Discussions about it (and all the devices that use its atomizer) dominate the forums. The 901 no longer is
as popular, but still has its place and many people prefer it. It's vapor generation is not as voluminous as the 510, but I get more TH from the 901.
There is more variation in sturdiness, quality, and effectiveness among individual units of the same model than there is between the 510 or 901.
No e-cig manufacturer has very good quality control.
Other than obvious differences in size, shape, and appearance, the most significant difference between models is the
feel of the vape: due primarily to the atomizer and secondarily to the power of the battery. With the advent of inexpensive
adapters a few months ago, you can use virtually any atomizer on any battery (including mods). My favorite non-mod skinny battery is the Kr8: 280 mAh and
true 3.7V (e.g., the 510 battery is 3.1V, the eGO is 3.4V). You can use the 901 atty on it without any adapter ... and, of course, use Kr8 cartomizers. Penstyle (e.g., 801) and 510 attys, among others, will work with adapters. In fact, my favorite non-mod configuration is the penstyle atomizer on a Kr8 battery.
So try out other atomizers, e.g., the 510, and see how you like them. You can get a full kit or just an atomizer and adapter. Once you settle in on the atomizer(s) you like best, you can get bigger and better batteries for it.