Affiliation is generally a closer and more formal connection than association is. I think affiliation is used more in the professional world than outside. There is a connotation of exclusivity with affiliation. If someone is affiliated with, say, one university, he or she is probably not affiliated with other schools.
(Also, regarding preposition choice, note that in the U.S. you would usually say or write that you are affiliated with or associated with a group of people.)
Expensive is behaving as a typical adjective, which are only modified by preceding degree words, e.g.
It was more expensive than...
It was more sudden than...
It was more amazing than...
If we pretend for a moment that is worth was a verb, we could compare it with some other verbs of measuring activites, e.g.
It weighs more than...
The room seats more people than...
It measures more than...
It costs more than...
The phrase is worth behaves likes a stative verb. The only other comparable phrase I can think of is [be] up/down as in:
The Lions are down three points.
The Lions are up more than the Bears were up at this point last week.
If worth is an adjective, then it is one which is almost always restricted to being a predicative adjective. This is how Oxford English Dictionary (OED) describes it, noting that it is used
Almost always (now only) in predicative use, or following the n. as part of a qualifying phrase.
What is interesting is that although an expression like
*Gold is more worth than silver.
with a preceding degree word, would be usually considered ungrammatical, there are several attestations listed in OED of exactly such a usage (where a degree word precedes worth) from the Early Modern English period:
1568 Newe Comedie Jacob & Esau ii. iv. C iv b, Ah sir, when one is hungry, good meat is much worth.
1581 G. Pettie tr. S. Guazzo Ciuile Conuersat. (1586) iii. 138 It may rightly be saide..that the feathers are more worth then the byrde.
1615 W. Lawson Country Housewifes Garden (1626) 6 Fruit blown vnripe, are small worth.
I'd say worth is an unusual word, and has only become more unusual in recent history.
Best Answer
The difference is qualitative versus quantitative. When you refer to higher quality, you say better and when you mean a bigger quantity, you say more.
In a casual use, when detail really doesn't matter, and you only mean one over another in a general sense, you may use either word in most contexts.
In the given context, prefer takes over instead:
"Many users prefer the look and feel of A over B."