Which camera to pick? - 1

Which ones?

Nikon D3000 or
Canon Rebel XS
or
Canon Digital Rebel XSi

it's for a digital photography class.

Have you read the professional reviews of those cameras on DP Review?

Have you compared the sensor performance on DXOmark?

After you do you own independent research, you should know which of them will be best for you.

All three are blah.

Buy a refurbished D3100 or T3. They are in the same price range.

The only advantage I can see with owning the D3000 is that it was the only time Nikon put on demand grid lines in the viewfinder on a D3X00 series camera. The D3100 and D3200 don't have this feature.

Grid lines are very helpful for landscape and architecture shots. As well as making sure your shots are level and properly framed in general.

I have a Rebel XSi, my son has an XS. Both excellent cameras but getting a little old now.

Can't help with the Nikon but of the 2 Canons the XSi would e better if only for the fact that it has a spot metering function that the XS does not.