If you are a complete idiot, don't use GPS...bettery yet, stay off the roads. People who've driven into lakes because the GPS told them to do it are idiots.
Once you apply a little common sense (check out the route before heading off, pay attention to signs to confirm the GPS appears to be giving reasonable directions, etc..), there is no question GPS is far better.
If you are worried about being routed thru bean fields, a pre-departure check of the route will typically eliminate that (of course, I've not seen many state maps detailing where the bean fields are). Also, there are GPS units that have a truck route option to keep you on major roads. (You can also set them to avoid freeways, toll roads and a number of other routing options, learn what your unit does and apply as you like)
In terms of map accuracy, there is no question. GPS has more detail and more accuracy and are updated more frequently. There is no way you are carrying a detailed street level map of every city you will pass thru. Likewise, if you get into a one way road system, the GPS while not perfect will almost always be better than a paper map.