They are actually owned by the same company. Marantz has been around for many years and offer high quality products. Honestly when it comes down to Denon, Yamaha, Onkyo and Marantz picking any of them will get you a solid product. In many cases it comes down to some of the small features like ipod connectivity, ethernet or number of HDMI connections.
Now just looked at the 1910 vs. the 5003 I would go with the 5003.
The big deal breaker on the 1910 is the lack of pre-outs. So if you ever wanted to add an amplifier you would not be able to do so with the 1910.