so using your reasoning above, then you shouldn't be looking at steel tanks because almost all of them are neutral or sink, especially with large gas volumes. If you believe in that system, then you have no choice but to dive AL tanks. In the US and for cave diving, that is impossible to adhere to, so we tend to prefer steels.
In the US my favorite example is this.
AL80 without valve is 26" tall x7.25" diameter and weighs 32lbs, plus it requires almost 5lbs to make it neutral for a total full weight of somewhere around 45lbs for 77.4cf of gas.
LP72 without valve, is 25" tall x 6.9" diameter and weighs 26lbs, requires no lead to make it neutral, for a total full weight of somewhere around 34lbs, and carries 71.9cf of gas.
The LP72 holds about the same amount of gas, is smaller in both height and diameter, but saves the diver from having to carry an extra 10lbs for no reason. The LP72's aren't around anymore, but the Faber FX71's which are 9l's hold the same math except are 21" tall.
In cave country, we need gas volume, so I can use a 19l tank, which holds twice the gas of an AL80. So my option is to carry a pair of 19l's, or 4 al80's to get the same amount of gas. The 19l is much more efficient, so we don't dive AL as primary bottles.
The tanks will only be below you if they aren't rigged properly, the only reason to dive AL bottles is if they aren't available to you, or you believe in handing off your primary bottles with your buddy in an OOA scenario.