A lot of this depends on how much maintenace you do yourself. DIY oil changes are a must if you want to save money because the Triumph oil runs you about $50/gallon. Doing it yourself, you can buy some Mobil 1 or other brand and cut that cost in half or more.
I have a 2003 Speedmaster with 27,000 miles on it, and outside of routine maintenace I've had little to do on the bike. Valve adjustments are the biggest cost if you can't do them yourself, about $250 every 12,000 miles. Maintenance costs between each dealer can vary. Might want to ask what your local dealer charges before buying. If you're looking at a shaft drive Shadow, you can save dough there over a chain drive.
As for reliability, I think it'll be hard to beat these Triumph twins. Since starting to make our bikes, Triumph has seen fit to lengthen the service intervals from every 4,000 miles to every 6,000 miles. Valve adjustments went from 8,000 miles to 12,000 miles.
I've been around this site for 2 years now, and I can't remember anyone blowing up their motor. However, I just had a quick look at a Honda Shadow board and came across this post:
"What he[mechanic] found is that the crosshatching on the rear cylinder was crap from the factory and the front cylinder was bad also, just not quite as bad. I now have a shot top end with 21,000 miles. He said it would take a total top end rebuild. New pistons, etc..I called the Honda dealer in Pasedena, Texas and talked to the service department. They said yes, they have dealt with several Aeros with the same problem from the factory and it will require a top end rebuild."
Now that doesn't sound like a reliable bike to me. The only caveat to buying one of these Triumphs is the aftermarket is slim on them. So if you like to just flip open the JC Whitney catalog and find 10 different sissy bars to choose from, then a Triumph isn't your bike. If you want something unique that won't see very often, then get a Triumph.
But really you shouldn't be making this decision based on maintenace intervals alone. Go sit on each and take one for a spin if you can. Buying a motorycle should be a visceral decision...one based on what your heart tells you. A motorcycle isn't like a car. For most of us it's a recreational thing, something you ride for fun. Whatever you choose, good luck and ride safe.
