Energy has a good reputation. I’m not sure about Polk, I think they have a reputation as being decent but I don’t know if they’re known for being the best. That Monitor series seems to be the cheapest series of real speakers from a decent manufacturer. I haven’t heard them or seen a pro review, but they get good user reviews so they should be good for the price, at least.
NHT makes good speakers, but they only have one small pair that comes in under $400. (these) NHT speakers tend to have low efficiency or sensitivity, meaning they don’t go as loud on a given amount of power. Those linked ones could work in a small room, but they aren’t the best choice for filling a large room like yours with loud sound due to the single 5.25" woofer and the low efficiency.
Klipsch is known for making high-efficiency speakers, so they may be a good choice if you want it loud but they don’t generally have fidelity quite as good as some of these other brands.
Don’t get caught up in specs unless you really want to take the time to understand them. A little knowledge is a dangerous thing. I’d go by reviews, reputation and you should get a chance to listen to them yourself; at least there should be a return policy if you order online. Speakers with bigger or more woofers will generally be able to handle bass better at high volumes, because even when you’re using a subwoofer the main speakers have to handle the upper bass and some of the middle bass.
You do need to check the minimum impedance that you receiver can drive. If you drive speakers with lower impedance than that, the amp could overheat (hopefully it would shut itself off) if you play them loud for a long time.
For magazine reviews I’d recommend Stereophile and Soundstage. They both do objective measurements which help to cut through the bullshit. Even if you don’t understand them, John Atkinson of Stereophile makes comments at the end of his measurements on whether they’re good or bad.
If you’re going to do surround sound, you may want a new receiver as the new ones have all sort of useful features, often including auto calibration using a microphone. They also have better ways of generating surround sound from a stereo source, such as Pro Logic 2.
If you’re comparing speakers in a store, try to get them set at the same volume. Otherwise, the louder pair will usually sound better just because it’s louder. Or course, you might also want to test how loud they can get, but for general sound quality you want to compare them at equal volume.