The smaller the monitor and the higher the resolution the better your game will look and the less anti-aliasing (AA) you would need. Meaning that (I know this from experience, see my own system specs) you can game on a 1920x1200 17"monitor with NO AA and the game will look much better than at 1680x1050 with 2xAA.
AA reduces the 'jaggies'. In-game you might see diagonal lines appearing as jagged and not straight like were you to draw them with a ruler. AA uses up a lot of the vram (memory in MB) of your video card. Ie if your video card is 512MB you can use more AA and enjoy better gameplay than were your video card 256MB.
Basically no one here can answer your question as yet because we don't know what graphics card you got powering your 1280x1024 monitor. It will also help if you post which types of games you like to play since some games are much more power-demanding than others.
At the end of the day, what one needs to check is the physical amount of pixels your graphics card has to work to create an image.
i.e. for your current monitor it's 1280x1024=1,310,720 pixels.
If you buy a 22" monitor @ 1680x1050 that's = 1,764,000 pixels.
A monitor @ 1920x1200 would soar up to 2,304,000 pixels meaning nearly twice as much as your current 1280x1024. But then if you needed to pump up the AA to the max on your old monitor you might only need 2x AA on the 1920x1200 or even none at all.