Which tank to use?

[eric myers 2]

If you plan on deep diving you may wish to consider:
1) Bigger can be better:

You could get a 100 cuft AL above that you are looking at steel.

You could get a 120 cuft ST in either High Pressure (3500PSI) or Low Pressure (2640 psi), theoretically these tanks will last same amount of time at a given depth all else being equal. However, from personal experience I can tell you a 120 HP seems to last just a bit longer. I am not biased because I have and use both. Although, the industry seems to have gone away from HP, for the most part. One big disadvantage of HP in MN is that some of the "out-there" shops can't completly fill HP tanks.There are some advantages to LP though. Lower working pressure usually means less stress on the whole system and that might tranlate into a longer equipment life.

2) Redundancy is important:

Consider a fully redundant pony bottle with its own regulator for deep diving or other challenging environments.

If you plan to attend a few fun dives and you don't plan on diving "deep." You might consider buying one or two AL's

1.) They are cheaper
2.) They are lighter
3.) They are an industry standard
4.) The first tank most people buy is an 80AL cuft
5.) In MN, freshwater, they seem to last forever if you take care of them (5yr Hydro, 1 year VIP). 
6.) You can almost always find a buyer for used ALs so resale may help you by that next new tank.