Episode #125 of the Stack Overflow podcast is here. We talk Tilde Club and mechanical keyboards. Listen now
6 of 6 added 12 characters in body

Ruby, 66 52 (shows only which one is longer)

f=->{gets.gsub(/./,?1)}
a=f[]
b=f[]
puts'sab'[a<=>b]

Prints s for same, a for string a, and b for string b.

Ruby, 184 173 146 143 139 140 (also shows how much longer it is)

f=->{gets.gsub(/./,?1)}
a=f[]
b=f[]
d=->e{Math.log10(e.to_i).floor.next.to_s}
puts(a==b ? ?s:(c=a.sub(b,''))!=a ? ?a+d[c]:?b+d[b.sub(a,'')])

Sample run:

c:\a\ruby>stringcmp
testing123
testing
a3

c:\a\ruby>stringcmp
codegolf.SE
code golf . stack exchange
b15

c:\a\ruby>stringcmp
test
test
s

c:\a\ruby>