two way or three way speakers

First understand that bass rarely will load in a room in the same plain as the mids and highs. Also controling bass resonance in the same cabinet as mids/highs is expensive.

Deep or powerful bass requires a lot more power than mids/highs, requiring a separate amp.

Most internal XOs are a compromise based on the designers room, equipment and listening bias.

When you want to get at hi-end magic get a pair of Magnepan 3.5R or better, or Emerald Physics CS2s where you biamp (and maybe still incorporate a powered sub) cutting off the frequencies via the active XO. This allows you to adjust for room, components, listening bias, etc.

SF, Franco Serblin says the center speaker only complicates things and he prefers the simple two channel speaker. would the same theory apply to two and three way speakers?

I'd agree - unless you can get a center channels woofer and tweeter at exactly the same height as the left and right speakers then you will be better off in phantom and putting more money into L & R speakers (for mostly one or two people watching movies - if you always have a crowd over then you will need a center to help listeners on the extremities of the sweetspot - you can always disable it when you are alone)

I'd second what Shadorne said. If it's not implemented properly, then the more variables you introduce, the greater that something will mess things up. As a matter of practicality though, more speakers may be needed in a room with a lot of people.

If your L and R speakers are set up properly, and you're sitting in the right spot, you don't need a centre speaker. There should be a stereo image of somebody speaking in between the L and R speakers. That's what a stereo does in the first place and why two speakers are used, i.e. to produce a "stereo" image and a soundstage. Otherwise, just use a single speaker in mono.

Also, if you have large full range speakers with deep bass response, you don't need a sub.

By the way, two-way and three-way speakers, as in your thread title, is not the same thing as using two or three speakers.