Flooring Tile - Tile removal vs. Tiling over

Currently, my kitchen and entry way have older ceramic tile layed over a concrete slab subfloor. Several of the tiles are chipped and others have become a tad loose. I'm looking to lay down new tile, but am not sure whether to take up the old tile and re-tile over the slab or tile directly over the current tile (which, with the exception of the a few chipped or loose squares, is in decent shape). Which do you suggest and, based on your suggestions, what's the best way to take up the tile and clean the subfloor or tile over the existing tile?

Thanks so much for your suggestions.

If you choose to tile over tile you need to fix the loose ones.
You will then rough up the surface with a belt sander or grinder.
Use latex modified thinset to tile over tile.
(my opinion: use latex modified thinsets always , it is worth the small extra cost)

If you have a dishwasher in the kitchen, the 2nd layer might make it difficult to remove and replace if needed. Also consider clearances for doors ect. Does the tile meet carpet ?

To remove, get a chisel and hammer and go at it or rent an electric jack hammer. Besure to wear eye protection.

Some times the old thinset comes off the floor, sometimes the tiles come off the thinset and leave most of the thinset behind.
If that is the case you can use some latex modified thinset with a flat trowell and skim coat the entire floor to create a smooth surface to lay the new tile on.