As a nyc native I have not stayed at the Sheraton LGA but I have heard it is better then one would expect.

I HIGHLY recommend exploring the neighborhood as it is the largest China town in the US and has amazing authentic cuisine from almost every region in China.

Check out Spicey & Tastey, one of my favorites. Regarding traffic into LGA it should never be more then 10 or 15 minutes, its really close and easy to do on the back roads. Count on the 7 train always being much much faster into midtown then a cab.