funkyguy4000:
By functionality, you mean if you want high speed or low power consumption, chow how much faster is TTL over CMOS?
Anymore, you will not know unless you read the datasheet for the specific part. It's no longer true that CMOS is always slower than TTL because there are so many newer packages that were never made into TTL and that run at really high speeds. Read the datasheets for the parts in question. Propogation delays are usually on the top half of the first page, you won't have to go far into it.
There are also some voltage differences and CMOS can be run at higher voltages. In fact, some packages run faster at higher voltages. Of course if you are running your system at 10V-15V to take advantage it better be all TTL or have level converters in it. Not all CMOS chips can be run at these voltages, check the datasheet.
More information:
More information still:
http://www.kpsec.freeuk.com/components/74series.htm
http://www.kpsec.freeuk.com/components/cmos.htm