Definetely preference. As an example, I have a male bell that I am absolutely in love with! Fantastic pattern. And I have a few trempers that are gorgeous too!
It comes down to personal preference, really. Each has their own look and features that attracts different people's eyes. Tremper Albino however, being the 1st strand of albinism discovered, is more of a "universal" albino in Leopard Geckos... Meaning that they are what you tend to see most of. If you go to a pet store, 9 out of 10 times, if they have an albino in there for sale, it's a Tremper. And alot of the combo morphs out there, if they have a strand of albinism in them, it is Tremper. However, some would argue thats not necessarily the case anymore, as Bells are becoming more prominent and more widely used. Rainwaters are typically the least popular amongst people (this alone might be what appeals to certain people and make them say they are "better"), but i'd say that is changing aswell.
I say bell! they have stronger colores and I think there eyes are more beutiful and the combos with bell have stronger color then tremper ones(SSB, sunglo, tanglo)
and too "Gekkon" you cant cross bells with trempers but you cant cross tremper with bell too XD(if too say the trush you can cross them but many people prefar not doing that...)