LP or HP tank?

[Vtach]

LP are usually bigger and heavier (for the same comparable volume as HP) but if you have your own fill station or find a willing dive shop, you can overfill them and get a good amount of extra gas.  The larger size LP cylinders do not work well in jacket style BC's, they are tall, heavy and cumbersome.

HP you rarely will get a fill that will maximize the full potential of what the cylinder is rated for.  Most cases you will find they will cool down to below the rated pressure.  I don't see too many downsides other than that.