Building up an all-city nature boy frame. Using Suginio RD cranksets. Need a 68x103 bb. Don't want to splurge on a phil wood, but dont want cheapy shimano either.

What is the deal with alum vs plastic cups? I am looking at sugino bottom brackets, some have both side plastic cups, other have both sides alum--both priced the same. Is one better than the other?

Also, is the origin 8 BB any good?

thanks.