dry tops.. dunno what to do..

[GonnaCatchABig1]

so let's say IN THEORY, i was planning on getting some new breathables and a dry top. in theory. the waders i can figure out. since i've destroyed a pair already, thus knowing which areas and feature to look out for this time around. but dry tops have me a bit confused, since i've never had one.
what should be lookin for? non of them are exactly cheap. but what type of bells and whistles justify the prices? (other than the obvious keeping you dry) what are the specific MUST HAVE features. as well the can make do with out features.
also is there any difference between the terms "dry top" and "wading jacket" or "slash top"?
kind of confused.
take two aquaskinz products for instance. the new raptor dry top... it looks and sounds like you could go scuba diving in the thing and not get wet. where as the nor easter looks and sounds more like a jacket that just happens to do a good job at keeping water out.

are these more water resistant than water proof? or do they seal up tighter than a (insert yer own ending)?

just wondering if the benefits are worth the hefty price tags. cause i did fairly well keeping warm in doubled up sweat shirts tucked into my waders last fall. didn't stay very dry. but stayed warm just the same.