I think youll find alot of opinions on viewing order. IMO, I like to watch them in the order they were originally aired. It does mean you jump around the timelines a little, but all secrets would be preserved this way:
The Gathering (pilot)
In the Beginning
River of Souls
Call to Arms
Legend of the Rangers
The Lost Tales
When you rewatch the series, you could change up the order to be chronologically correct.
Just my opinion of course!
I agree with this order for a first-time viewer. One, it makes it MUCH easier for the viewer to get the disks, and two, well, it just doesn't break up the flow of the episodes.
The movies are, save one, self-contained. They do not add to the *big* story arc (and this series sure has one, though I doubt a viewer in season 1 has caught on to it quite yet), and do tend to break up the flow. There's one that does that pretty bad. Sure the timeline says it goes between episodes (actually, the events supposedly occur *during* the episode, between commercial breaks).
The first-time viewer probably isn't going to want to stop a dvd mid-episode, put in another disk to watch a movie, then go back and try to figure out where that break is. What's the point in all that hassle? Just watch em in the order described above and you'll be fine.
Heck, you could probably save "The Gathering" movie til later and just do watch all the movies in order after the end of season 5. It'll be a nice little treat, seeing old familiar faces from so long ago.