I would say the mains, esp. if you listen to music often liked mentioned above. I am currently not even using a center speaker; I suppose you could say I am missing out on movies. The main reason I do not have one is because my front speakers are some older Advents, and it would be very hard to find a center to match them. I plan on upgrading all my speakers (besides my sub) in the future, but not any time soon, so I will live without one. IMO the importance of speakers goes mains, sub, center, surrounds. I am sure that many may disagree with that and that’s fine.
Dialogue: center channel Music: fronts Effects: surrounds/sub.
The center channel is important as it carries the dialogue, but I disagree with the sub being the second most important speaker; this depends greatly on the types of movies that one enjoys.
anyways, IMO (and this goes against a lot of opinions here), getting a good front pair (and well, most preferably the matching center) is most important.
- You don't "need" a center channel. It is much preferred of course, especially if there are multiple viewers. However if there is only one viewer, s/he can always sit in the sweet spot.
- A good front pair can make the need of a good Center (subject to the caveat above) and a sub almost redundant. I say almost, but you can get a heckuva lot of milage out a great front pair; more IMO than a great center and a sub.
For a movie setup I think it's important to choose the front 3 speakers as a single entity. Ideally the same speaker, or quite similar. That gets you a seamless front soundstage where the speakers seem to dissappear.
Sub and redundant are two words I'll never group together. Movies without deep bass aren't worth watching.
If I had to go in steps, and movies were the priority,
center (with an eye towards suitable mains later) mains sub surrounds (any old pair of bookshelfs do well here for awhile)
There is nothing worse than suffering with a mediocre center channel that smears dialogue.
I've read that approx. 70-80% of most movie's content is center channel. Me, I'd get a great set of mains from a manufacturer that offers a good center to match. For me, music listening is still the main priority and you don't need a center for that, but you certainly need the mains. You can also do a very effective phantom center with just the mains for movies. As long as you are sitting center, it will actually sound bettern than all but the best center speakers.
The "Front Three" are vital for home theater. The front three provides a solid, front soundstage which allows for smooth L-C-R panning. Also, 99% of all on-screen dialogue comes from the center channel.
You can get by w/a pair of crappy surrounds if your "front three" are a good, timber-matched trio.
For stereo listening, you don't need a center channel at all. Nuff said there.
In a home theater, you will notice almost all of the sound comes from the center. You will probably be amazed at how secondary the mains become! They are obviously important, but having a small center and big mains in a HT system is not ideal, and the center takes most of the action.
Look at HTiB systems - in many cases, the center is a much bigger speaker because it is more important.
Well, I think that is 70-80% of the movie dialog is from the center channel. Hence, the center is important for movies and fronts important for music. Though, movie scores and sound effects do occupy the fronts also.
If you find yourself watching a movie and are turning up the volume because you "can't hear what they are saying," recalibrate your speaker levels and you may find the center a little low. It is important for the dialog.
Both Main and Center should be thought of as equally important in a home theatre. If your trying to figure out which to purchase first, then you might be able to get away with the TV volume for the center until you can afford the center channel that compliments the mains, but ultimately you'll need a center that can keep up with the mains. In an action movie, your mains will produce a good deal of sound. Use a sound meter to balance your system using a test tone.
The thing about posts like this, is that so many people replies with "mains can be run in phantom mode, so they are more important". This is very true, but I think most people that ask this question are going to get all three front speakers and are wondering what is the best way to distribute their money. If this is the case, I would say center for movies and mains for music. In my system, I had three identical speakers for my L,C,R (Cambridge Soundworks MC300's which are dual 4"woofers and one 1"tweeter). They have amazing sound quality, but don't have the umph for my larger living room. I upgraded my mains to larger bookshelves, but because of changes in my living room, I had to go on wall for my mains, so I traded back the bookshelves for the MC300 satellites. I used the upgrade money to put towards a larger and better center.
Since I had tried both, my personal experience was for movie watching, things sounded much better with the bigger center and smaller mains than it did with the smaller center and larger mains. For what it is worth, I also like my current setup better than identical speakers for the front three. I was very worried about this, but since all three speakers are from the same line with identical tweeters, I have no issues with voice matching and panning.
I made a very lengthy post on the AVS forum which I will have to search for about selecting speakers/subwoofer for a home theater. The super-short-summary is simply this: Start by selecting a great center for your needs that also has a suitable matching L/R (or even use the center for all 3!). Then size an appropriate subwoofer for your space. This should be your priority in improving the quality of your system, with the center, sub, L&R followed by the surrounds in this respective order.
A very comical demo is to take a pair of cheapo L&R speakers mixed with a great center such that the listeners can't see the L/R. Couple this with a great sub and while the L & R mains add a great deal to the mix, I would rather have this mismatch up front than live with 3 of the matching cheapo speakers as L/C/R.