Heynow said "Centre channel is the most important...Sub woofer is second most important. If you're asking for advice then you're likely best sticking with something in a 5.1 channel (2 fronts, 2 rears, 1 centre and a subwoofer). Speakers will make no real difference for someone who isn't REALLY into it. Think of it like all those 20 year old Honda civics with tin can mufflers and carbon fibre hoods and 20 year old engines with 300,000kms on them. Unless you're going to buy a $1000 amplifier there's no point buying $2000 worth of speakers.
I'd say go to Best Buy and buy an amplifier with these things
1.) at least 4 HDMI inputs
2.) 4K support
3.) Wi Fi
4.) 5.1 channels
You'll be around $400 for a good one. Get the most affordable speakers you can get and buy a $150'ish sub woofer. Don't let them up sell you or make you think you need anything fancy. Doesn't matter what kind of Sub woofer you buy. Personal opinion but Extreme is going to sell you a lot of stuff you don't need, and Best Buy has next to know expertise in anything. Not their fault they just don't have 20 year stereo guys or people with any interest in electronics working there. I'd recommend Aurora actually, if I had to send you anywhere. "
I disagree with almost everything said. The speakers are THE MOST IMPORTANT PART of the system, and a $150 sub is going to be GARBAGE. I just purchased a $1250 subwoofer for my 2 channel listening system, so I might be a tad biased.
We need to know a few things. What is your total budget, how big is the room, and are you going to piss anyone off with this system (apartment, neighbors etc).