I have another question, assume i get 200watt Sub, and reduce the Sub to 100w for my use, will I get same effects that I get from actual 100w sub with reduced 100watt Sub or will the effects will reduce in reduced 100watt sub while compare to actual 100watt sub..
The room is about medium sized ~20sqm. Don´t worry about the wattages. You can´t choose sub based on power figures.
From those two you mentioned SVS PB1000 should be more enjoyable sub for movies cause the QA sub won´t have much output under 30hz which many considers quite important range with blockbuster movies. Second thing you get bit more impact from ported sub (PB1000). But as you live in apartment the question will be can you enjoy it fully. If you don´t have neighbours under you then chances are you will be fine using common sense with the volume. If you want something compact without "rumble" then SVS SB1000 looks bit better than QA QB12 cause you get the long amp warranty and support with SVS is best in business! Don´t know if these prices are best there:
Extreme depth, power and intensity of a world-class subwoofer, from a super compact 13-inch cabinet. The SVS SB-1000 subwoofer is small enough to conceal in any room, and with its 12-inch front-firing driver and 300 watts RMS, 700+ watts peak power amplifier, energizes a room with deep...
In terms of performance I think the SVS subs are the ones to get. If I was spending £500 that would be top of my list. I have the SVS SB3000 in a room a similar size to yours and that's more than enough. I could have probably got away with a lower model I think.