First of all if you have trouble keeping your head out of the water wearing a nearly empty AL tank you are WAY over weighted. AL tanks become more buoyant as the gas in them is used so if the tank is nearly empty and you have trouble keeping you head above water, GET RID OF SOME LEAD.
Now for my opinion. I've dived with both types of tanks for recreational diving using both air and Nitrox and IMO I would say HP 100's no questions asked. They are smaller, lighter, and easier to handle than LP tanks of similar capacity. Nearly the same size as an AL 80. Most dive shops, if not all, in this area have no trouble filling an HP tank but not all will over fill a LP to give you an equivalent amount of gas. And if you get into Nitrox in the future there's no trouble filling an HP with a recreational mix of 32 to 40%. There's no trouble filling an LP either but some folks will tell you that the gas laws of compressability come into play when using HP tanks. This can be true if you're using TriMix but that's a whole nother animal and something you don't need to even worry about right now.
The extra volume of gas you get with the 100 cuft tanks will allow you that 800 psi you're looking for while not effecting your bottom time much at all. And again if you get the Nirox certification you wouldn't believe the amount of time you're able to spend on the bottom and still surface with plenty of gas in reserve.
Just my 2 psi worth.
Now for my opinion. I've dived with both types of tanks for recreational diving using both air and Nitrox and IMO I would say HP 100's no questions asked. They are smaller, lighter, and easier to handle than LP tanks of similar capacity. Nearly the same size as an AL 80. Most dive shops, if not all, in this area have no trouble filling an HP tank but not all will over fill a LP to give you an equivalent amount of gas. And if you get into Nitrox in the future there's no trouble filling an HP with a recreational mix of 32 to 40%. There's no trouble filling an LP either but some folks will tell you that the gas laws of compressability come into play when using HP tanks. This can be true if you're using TriMix but that's a whole nother animal and something you don't need to even worry about right now.
The extra volume of gas you get with the 100 cuft tanks will allow you that 800 psi you're looking for while not effecting your bottom time much at all. And again if you get the Nirox certification you wouldn't believe the amount of time you're able to spend on the bottom and still surface with plenty of gas in reserve.
Just my 2 psi worth.