Best microphone picking up sound within a small room?
You need to pay attention to the following items:


High sensitivity - measured in dB, and always negative.  You want a value closer to 0.  That is to say that -38 is better than -44.  Sensitivity is measured relative to a given pressure and voltage.  0dB would mean your microphone is as sensitive as the standard in the definition.  See this article from the Arrow site (actually linked on the microphone pages you posted.)
High signal to noise ratio - the microphone (and its internal amplifier) produce noise.  You want as little noise as possible, else it will drown the quieter signals from across the room.  This is also measured in dB, but positive numbers.  You want the highest you can find.  60dB is better than 55dB.
Directionality - if your device is on one side of the room and you want to pick up sounds from the other side of the room, then you will want a cardioid microphone rather than an omnidirectional (make sure it faces the correct direction.) If you need to pick up sounds from all around, then stick with omnidirectional microphones.
Amplification - even the best microphone will have a low level output.  You will want a good, low noise amplifier between the microphone and the sound card.  You could use gain (multiplication) on the digital data from the sound card, but the sound cards are usually noisy so you would be amplifying the noise as well as the signal - your signal to noise ratio will stay the same (or get worse.) I'd find a pre-amplifier that can take microphone signals to line level and use the line in on the sound card.  You said you tried an amplifier and it made it worse - well, too much amplification is bad, and a bad amplifier (poor signal to noise ratio) would hurt things, too.
Automatic gain control - if you are trying to make recordings of sounds from all over the room, then the volume will vary greatly.  The further the source is from the microphone, the lower the level.  AGC attempts to keep the recorded sound level approximately the same.  You can do this in software or as part of the pre-amplifier.


Points 4 and 5 are obviously not part of the microphone, but are parts of the system you are building.



If you use the microphone input of the sound card, then it expects a low level signal.  An amplifier intended for line level would produce a signal far above what is expected.  You would then hear a lot of noise, and extremely distorted speech.

You can usually change the gain of an amplifier.  If the circuit you use provides too much amplification, then you could post the circuit here (new question) and ask how to change its gain.

Or, use the same amplifier on the line in input of the sound card.  Some (many?) cheap USB sound cards only have a microphone in, though.

Your microphone is most likely picking up sounds from all around the room - you just can't hear it.  Record using Audacity, then use Audacity to increase the volume (try the normalize effect.) I think you will find that your signal is there even without a pre-amplifier, though it may be too close to the noise floor of the sound card to be useful.