I've used Nobeltec VNS for a long time and really like it, but I can't
recommend it any longer because of their constant upgrade policy. Just
like Windoz, they come out with a new version maybe every 18 months or
so, and pretty much force you to upgrade, dropping support for older
versions as they go. The final insult was when they went to DVD only
for upgrades and charts... my navigation computer doesn't have a DVD
and I don't plan to add one.

I've heard nothing but good about Cap'n, and Rosepoint's new product
seems very well built as well: http://www.rosepointnav.com/default.htm
If I were starting over today, I'd probably go with Rosepoint.