I was teached that the more "roman" way is to wear a cassock, then Why albs?? I believed albs are for ordained ministers; or is because in LTM an altar server is an "ordained"
First of all, the acolyte would still wear a cassock under the alb. It's true that wearing a surplice has become an established Roman practice, but all a surplice is is an abbreviated alb. They both signify the same thing (baptismal purity). The alb is proper to all Christians, not just ordained ministers; a baby traditionally wears a white garment to represent the alb, and an adult receives an alb if he's baptized then.
I say albs are preferable to surplices since they're fuller garments, the same way I prefer fuller chasubles than fiddlebacks, which are like the sleeveless t-shirts of vestments in my opinion. But for low Mass as opposed to solemn, surplices are okay since they're easier to put on.
The cassock/surplice combination, by the way, is more appropriately called choir dress. That's what clerics wear when they sit in choir. So it's appropriate for a Gregorian schola to wear, or for the master of ceremonies since that role is unofficial and optional.