We originally just had netflix, but recently subscribed to hulu plus too...
Basically, for movies, netflix is great. For TV shows, Hulu is great for filling in where Netflix leaves off... example: Wife wanted to see Hot in Cleveland. We watched it on Netflix til a certain episode. After subscribing to Hulu Plus we got to see the episodes after that one over on hulu plus.
Free version of Hulu is better than Hulu Plus based on what I've read about it, but not for the newer stuff... just for wider variety of older shows, etc.
I too dislike Hulu's ads, but at least there are not a lot of them.
(uh, you can get the free version of Hulu on Roku if you use Playon, but we decided to not go that route lately because it puts too much stress on the computer... also decided this because my wife wants the latest episodes of shows, etc.)
Biggest disadvantage of Hulu Plus: It does not remember which episode you were on in a series. It also only has certain number of episodes on any series. However, it does have a neat way of organizing it that lets you have access to more than 500 things at a time unlike Netflix.
Biggest disadvantage of Netflix: You can only have 500 items in the queue at any time. Sounds like a lot, but really it's not, especially if you watch a lot of stuff like tv shows, stand up comedians, and other stuff like that which is not full length movies, etc.
If you get netflix, go ahead and get the channel that nowhere man put together to find more stuff in netflix since that thing works better than the netflix website for finding stuff, but it's also a little of a pain since it's so painfully slow in adding stuff as it it sits there and does what it's doing to add it to your queue.
I'd also recommend looking into Crackle. It's free from Sony and while the content is sparse it rotates new stuff in from time to time and the ads are short and tolerable. Think of it as Hulu Jr.
I'd recommend crackle, popcornflix, vanguard (think that's the name of that independent channel?), openfilm channel (even if some of the stuff is odd internet stuff), and also noknok, and a few others... It's nice having options.
http://forums.roku.com/viewtopic.php?f=28&t=46566&p=359897#p359897 -channel lists/tools
http://forums.roku.com/viewtopic.php?f=28&t=64096 -linear channels