Glass rods are better for trolling for a few reasons:
First of all the price, glass are way cheaper than graphite rods.
Secondly there is no difference in sensitivity when you place your rod in a rod holder. We all know that graphite is much more sensitive then glass but not a factor in trolling. Glass is heavier then graphite so this is also not a factor unless you are holding the rod in your hand for prolonged periods of trolling.
Thirdly, glass is muce more durable and flexes more when you get a strike making them last much longer during the constant stresses of trolling where as graphite rods will not hold up to the constant strain produced by trolling.
IMHO buy a glass rod, either a Shakespeare Ugly Stik or a Shimano Compre.
Dirk