Joined: Feb 2013
Posts: 1,472
Likes: 11
From: Near St. Louis, Missouri
Bikes: Giant Defy Advanced, Breezer Doppler Team, Schwinn Twinn Tandem, Windsor Tourist, 1954 JC Higgens
The saddle IF it isn't working for you.
Pedals if you don't already have clipless pedals on it.
Otherwise upgrade when you need to replace something that's broke or worn out.
Tires or the chain will probably be first to go. There isn't all that much difference in chains, but there are choices in tires.
Next may be brake pads. KoolStop pads can make a difference.