I have a 28' Bayliner that weighs 9,000lbs with a pulpit and a 25lb claw(with 30' of 1/4"chain) with a 22lb danforth (w/ 40' of 1/4" chain) as a backup
In my experience (Which does NOT include rivers) the Danforth works ok in the lakes and ocean on sandy bottoms, if there is millfoil or grass on the bottom a danforth will cut into it and give you a good set, but you have to stick to a 5 or 7 to one scope to get a good set (30' of water you need 150' to 210' of line, more chain can cut this back somewhat). If you want to change your style of anchor I would suggest a bruce or claw anchor
http://www.westmarine.com/webapp/wcs...01/212/11206/5 , its what I use after bending several danforths on rocks in the sound...The downside is that you would probably have to change your anchor roller to accomadate a claw type anchor, they usually will not work with a danforth style anchor roller/pulpit without modification at the least(although it may be as simple as putting a bungee cord on it to keep it from moving), and in grass and millfoil they can be impossible to get to set. Although I have never used one of the river anchors I have seen them and my uneducated guess would be that it might work with an anchor roller but I don't know about a bow pulpit.
In keeping with the "if it works don't change it" theory, my suggestion would be that if you have been using a river anchor and it works for you and how you use your boat then that would be the most important critera and stick with a river anchor and figure out how to make it work on your pulpit/roller. If you plan on doing more and want to change to another anchor or get a backup then you would have to make a decision based on your planned use.
West marine also has "west advisor" on their website, I would have included a link to it but their site has changed and I could not find the article that I was looking for that was very concise and easy to understand... what I did find is here and less than what I wanted but may help you decide on a different anchor or find a roller that will work with how you want to set things up
http://www.westmarine.com/webapp/wcs/sto...catalogId=10001