For the most part they are the same. Check this link.
http://www.yamaha.com/yec/products/receivers/receiver_main.htm
Click the what the difference... link on the bottom left.
The 5890 is this year's model, it has XM radio, while the new 1500 (1600?) is not out yet. If XM is your thing get the HTR-5890.
Keeping the XM thing out of the equation I'd still the RX-V1500 for it's looks.
Or better yet wait for the newer model RXV. Probably this summer is early fall.
