"Anchor size" is one of those threads that can go on forever. "What's your favorite anchor?" is the companion thread. It also goes on forever. However, both are important questions and should be discussed and debated. Please allow me to offer my 2 cents (If I mention a specific anchor in this post it is NOT and endorsement of any manufacturer or design! Pick whatever works best for you in your local conditions, not what works for me.)
I'm a firm believer in KISS; keep it simple stupid. My anchoring philosophy revolves around this principle. I'm also a firm believe in "practice makes perfect".
IMHO bigger is better. I have chosen anchors and rode rated for boats bigger than my Hunter30. Oversize anchors, attached to 12' of chain and nylon rode have worked for me in all types of conditions; from NY to the Bahamas I believe that the more anchor weight that hits the bottom, the deeper and quicker it will set.
As far as rodes go, unless you routinely anchor over coral reefs or other abrasive bottoms, I never understood the need for all-chain rodes. First, it adds a tremendous amount of weight to the bow of the vessel and it's a real PITA to retrieve without a good windlass. For the all-chain users, dropping a big pile of metal on the bottom does not constitute anchoring. It may work just fine in calm conditions, but as soon as the wind picks up and the chain plays out, you're SOL. Seems you never actually to set the anchor. Snorkel around a couple anchorages and you'll know what I mean.
I know, chain is stronger. But how many hurricanes to you plan to ride out in your vessel? The elasticity found in a nylon rode may help to make up for its different tensile strength.
The second most important part the anchoring equation is choosing the right anchor for the bottom conditions. Personally, I carry four anchors. My primary is a 35# Delta. My secondary is a 33# Bruce. Both are attached to 12 ft. of chain and 150 ft. nylon rodes. I also carry a 30# Danforth and a 15# claw anchor.
In the Bahamas I use the Delta almost exclusively. It penetrates sand quickly and is sharp enough to penetrate grass (especially if I dive on it to force it into the bottom) The Bruce is there in case I encounter a muddy bottom. It held like crazy on my last boat when I spent most of my time on the Hudson River. The claw anchor is collapsible and works great in a rocky area, or at the edge of a coral reef. The Danforth serves as my storm anchor.
Keeping to my KISS philosophy, I seldom deploy more than one anchor. I must admit that when a 40 knt. squall roared through my anchorage one morning, I motored into the wind for awhile to take the strain off the anchor . The next time the weather report called for similar conditions, I used the Bahamian moor to deploy both bow anchors. Everything worked just fine until I had to dive down to untangle the rodes. Same thing happened the next time I tried this technique in Nassau Harbour. For this reason I tend to anchor away from those folks who deploy two anchors. I will happily swing around my one anchor, keeping a regular anchor watch.
Laying out the proper scope is where many novices run into problems. For most situations, I find a 5:1 ratio to be sufficient. If a blow is expected, I'll go to 7:1 or greater. If you have any doubts, dive your anchor to see how your boat pulls on it. If your rode is lying flat against the bottom, any horizontal pull will serve to set the anchor more firmly. If the rode is rising clear of the bottom, the upward movement is apt to dislodge the anchor. Keep it simple. More wind, more rode.
Proper anchoring is not rocket science. It's common sense, reinforced by lots of practice.