There is no "best" It depends upon adherands (what you are gluing), exposure to water and heat/cold, type of stress it gets, requirements for open, closed and cure time, ability to clamp, initial "grab", need to reverse in the future, cost considerations, need for "stiffness" vs. creep vs. springback, fitness and cleanliness of joints, shelf life, pot life, application/curing temperature humidity, and so on.

Strength is not usually an issue -- most common glues are stronger than the wood around it it ATSM tests. And most common glues are within 10% of each other in shear strength. So proper application and joint preparation is much more important.

Resourcinol would be a good choice. As would epoxy and type-2 PVA (Titebond III or Gorilla Wood Glue (the white stuff, not the PU). I'm not a big fan of the Polyurethane (PU) Glues. I've just seen way too many failures of these "wonder products." I wonder why people use them.

Here is a link that might be useful: Glue Guide PDF

Epoxy.

And NOT the 5 minute type, it has poor water resistance.

Titebond II or III if you have otherwise good construction.

Would a PVC or plastic based glue work? I've basically just used the elmer's outdoor wood glue.

Here is a link that might be useful: Best CNC Machines

" I've basically just used the elmer's outdoor wood glue."

Not as well.

Plastic glues often have issues with creep under constant load.

Resorcinol and Casein wood glues will give good results in terms of strength and water resistance.

The quality of the joints is most important!

Mortice and tenon joints with draw pins are the best joint to use for long term use. Try to employ diagonal bracing (ornamental) in the framing to stop too much ricking on the joints.

Use draw pins (dowels) to pull the joints together once fitted.

The glue should be considered as a secondary element to assist in the actual joints performance.

Many years ago only animal wood glues were available and these were not considered to be of sufficient quality to hold construction joints together. Items had to be constructed in a way that they could rely mainly on the joints alone. Making good joints is the first thing to attend to then using a good quality waterproof glue second. If you apply both to your furniture you will have no long term joint problems.

I used "Casein glue" on a mahogany park bench which I made 33 years ago and it is still going strong.

Hope this helps.

"The quality of the joints is most important! "

Neither of these glues can be considered 'gap filling.'

If you have less then perfect joints, epoxy wins for exterior use.

Brickeyee,

An interesting point with epoxy glue is that it does require a slight gap in the joint to be properly effective. If there is insufficient epoxy in and around the joint the joint might fail. I guess it depends upon how a person likes to work which glue is ultimately used.

Epoxy, Resorcinol or Casein will all do the job pretty well.

There is nothing like liquid nails!

"An interesting point with epoxy glue is that it does require a slight gap in the joint to be properly effective. If there is insufficient epoxy in and around the joint the joint might fail. "

Rarely is to small a gap for epoxy a problem for new woodworkers.

Epoxy (and some of its close derivatives) remain the outdoor choice.

You can build boats with it.

This post was edited by brickeyee on Sun, Feb 17, 13 at 12:54

Nothing beats Liquid Nails??? Think again.

From
http://www.duspec.com/DuSpec2/product/ProductDocumentSearchController.htm?documentFormat=pdf&systemSetId=70&productCode=LN-903&documentType=datasheet

Shear Strength:
24 hours 150 psi
48 hours 180 psi
1 week 240 psi

Most woodworking glues are in the
3500-4000 PSI shear ATSM D-905 testing. Epoxies run 50-100% higher than those.

ref:

Here is a link that might be useful: Titebond glue guide