The No. 1 question I get from readers is something along the lines of "What's the best speaker?" Some readers include a price range, which is a huge help, but there are a lot of factors that should be considered when selecting a speaker. Or to be more precise, a speaker system.
Speakers "play" the room, so room size and acoustics should be taken into consideration when buying speakers. The pair of 8-inch tall speakers that might sound great in a 10-by-12-foot bedroom probably won't cut it in a 25-by-40-foot living room, where you might need a pair of heavyweight towers. Small speakers can sound great in small rooms, but if your room is bigger than 400 square feet I'd recommend large bookshelf or tower speakers. Few hi-fi speakers sound best up against or near a wall; they tend to work better when placed a few feet into the room. Most speakers sound best when their tweeters are positioned at or near the listeners' ear height. So practical placement options are crucial when shopping for speakers.
Before we go any further -- volume capability -- how loud you like to listen is also related to speaker and room size. Large rooms, or rooms with lots of sound absorbing materials such as thickly padded couches, heavy drapes, or plush carpeting soak up a lot of sound and power. Rooms with large exposed windows and bare floors reflect a lot of sound, and can sound "lively" with a lot fewer watts. Ideally, you want a balance of soft (sound absorbing) and hard (sound reflecting) surfaces.
Big speakers with lots of drivers that can easily dish up home-theater special effects and bombast may not be ideal for acoustic jazz and classical music. The fidelity requirements of explosions and gunfire are mostly concerned with loudness and dynamic range, reproducing the sound of a piano or acoustic guitar is completely different. I find that smaller speakers, or ones with just a single woofer, may be better suited to music. Sure, if you throw enough money at the problem you can get speakers that are terrific for music and home theater.
Bass quality and quantity requirements vary a lot. Some folks really want to feel the bass, some find powerful bass an annoyance. Again, room size plays a crucial role here, with the right set of speakers in really small rooms you may not need a subwoofer, and large rooms may need more than one sub.
For home-theater speaker buyers, I always recommend sticking with the same brand for the front, center, and surround channels. With subwoofers, that's less of a concern. If you'll be using your system primarily for movies, go for the best center-channel speaker you can afford. If music is the focus, put the majority of your home-theater speaker budget into the front left and right speakers. If you plan on listening to a lot more music than movies, stereo speakers will give the best return per dollar spent. For example, investing in the right $1,000 stereo speakers will produce better sound than any $1,000 5.1-channel home-theater speaker/subwoofer system. The logic here is straightforward: the more speakers you buy with a given amount of money, the lower quality each those speakers can be. Don't mistake quantity with quality.
As I said, the "best" speaker question comes up a lot, and I can always say what I like, but I can't predict what you'd like. The variables that determine the right speaker for a given buyer -- taste, room size, and the speaker's appearance -- complicate speaker shopping. Putting some thought into exactly what sort of speaker you're looking for before you start searching will eliminate a lot of dead ends.