Longer length of lighter chain for me. The important bit is the ratio of anchor rode length to depth. 4:1 is okay for the picnic ashore in good calm weather when you can see the boat. 5:1 getting better for an over night stop and greater if you can.
Don't forget the 1m from sea level to the top of your tubes if you must have the anchor warp going over the tube but not good practice, use a bow strong point instead.
This is quite a good article:
Fortress Anchors - Safe Anchoring Guide
Another excellent article on catenary:
Catenary & Scope In Anchor Rode: Anchor Systems For Small Boats
What ever anchor you choose, I would suggest avoiding pattern copies. The patent for the likes of the Delta has now expired so Chinese copies are appearing in chandlers at half the price, but the quality of the galvanising and welding is dreadful. CQR and Bruce are another two which are copied.
Some of the better makes, Delta, Fortress, Spade & Manson Supreme. Rocna was good but the quality of the steel is now suspect following the move of production to China and a cost cutting exercise.
Modern high holding anchors are excellent but expensive, however so would be a rib if the anchor dragged and she ended up on the rocks.
If weight and size are a problem, then the Fortress which strips right down and can be assembled in a minute has to be a good choice for a rib. Made from Aluminium and recommended for a chain / rope rode rather than all chain helping to keep the weight down.