Interesting - when I tried it, my Manson Supreme would not hold in weeds, nor would my CQR. The other two anchors I had on board were a 150lb Fisherman and an aluminum Fortress. I was sure the Fisherman would hold but since it is a pain to haul out and assemble (really bought for super heavy wind use), I tried my Fortress and it held. Maybe the difference here is how much chain you have. My rode is all chain and I made sure I had plenty scope. Anyway, anchoring seems to be like religion and politics. I am sure before long you will have seen every possible combination suggested. It may be best to see if you can borrow different types of anchors, make sure you have enough chain scope and try them all out to see what works best for your boat and situation.
A Danforth is probably about the worst since it has so much surface area for the weight. Beyond the anchor, a really important consideration is the technique. You want to not be moving at all so the anchor and chain can work down through the weed without picking up too much of the vegetation. If you are moving in any direction the anchor gets clogged with week before it even has a change to find the bottom.
If you're looking for a lunch hook, or something that you'll tend to, I like the grapnel idea. I would not sleep on one or leave for shore, however.
Grass is just an unreliable anchorage, no matter what. Even in the best circumstance, you may actually be set in a big knot of grass that you dragged a few feet and piled up. A few hours later, the grass lets go and you're loose.
We have a few anchorages with heavy grass, such as CuttyHunk. We will try to move around to find a gap or less grass, even if it means anchoring a bit further from shore, in deeper water or less protected from wind/waves. I would rather have a good set in a tough spot and than bad set in a good spot.
I'm going to go out on a limb here, and ask the obvious questions... so shoot me if this is too obvious (I am not trying to bust)... But do you have enough rode out? 5 or 6:1 at least? Do you have a decent amount of chain?
On my rather rocky lake in the few places that are soft/weeds, my danforth holds fine, but I use nearly 100 feet of rode, and 10 feet of chain for 15-20 feet of water. I've not had an issue with hold since I've upped the length of my chain from 6 feet. Granted we rarely have high winds, and most of our chop is produced from antique V6 outboards by wanna-be water-drag racers.