My bad, I forgot they switched from Symbian to Maemo relatively recently.
No, in all seriousness, the N900's not a bad phone at all, or more not a bad smart phone. Nor is Maemo or Symbian. From all I've seen its more of a pocket computer, a linuxy OQO with a phone added in. The N97 mini would be more of what I'd compare to the modern smart phone. It just has about as much affect on the U.S. Phone Market as Linux has in the U.S. Desktop market.
That said, iPhone is far from the most advanced OS that actually is a blip on the U.S. map. WinMo 6.5, Android, and WebOS all trounce it in regards to the capabilities in the hands of the users with regards to the OS.
The iPhoneOS is not about power though, and about usability. Which, by essentially stealing the old Palm OS and prettifying it while making it touch friendly, they've managed to do better than any others (Though personally I think even in ease of use WebOS is superior).
Though right now if I was going for a laptop replacement in a phone it'd have to be the HTC HD2, but then again it'd depend on why I was needing a legitimate mini-computer in my pocket.
Ultimately though, who needs a laptop replacement in a cell phone. I want my cell phone to do me well with my portable needs. I'll take a little netbook if I need a laptop for traveling.
The "Best" Smart Phone ultimately is the one that does what YOU want the best. The N900 may be the most versatile, it may have the best specs in your opinion, but it being the "best" is subjective based on a number of things from usability (both in the phone and in your area), what you plan to do wit hit, etc. The "My phone can do so much more than yours" was the trap PocketPC and later Windows Mobile fell into when battling against the old Palm OS and the early days of the smart phone market. Just cause you can do more, and have more, doesn't necessarily makes you "better"...just makes you more powerful.