Trivial Q, sorry

[zak seidov <zakseidov@yahoo.com>]

Dear PARI gurus,

I use (on a very trivial level)        
GP/PARI CALCULATOR Version 2.5.3 (released)
           i686 running mingw (ix86/GMP-5.0.1 kernel) 32-bit version
                    compiled: Oct  3 2012, gcc-4.6.3 (GCC)
               (readline not compiled in, extended help enabled)

in Windows 7. 

Calcs are trivial but lengthy,
so one of my Qs
from point of speed, is
what is better to use 
a) variable for some (large integer) constant,
say a = 123456789987654321
or
b) constant 123456789987654321 itself?
Thanks,
Zak