The torch type follows from current and cooling. Type 9 works up to about 80 A and is the slimmest, so it reaches where others cannot. Type 17 is the universal gas cooled torch up to 150 A, type 26 up to 200 A, both for intermittent work. Type 18 is water cooled and runs continuously up to 350 A, type 20 is its slimmer equivalent up to 250 A.
Above 150 A and for work longer than a few minutes, move to water cooling. A gas cooled torch at that load heats the handle and forces breaks, and the cable loses flexibility. A cooler with a pump delivering 3 to 5 litres per minute is enough for most manual torches.
A flexible head helps with positional work and with parts of changing geometry, because you set the head at an angle without twisting your wrist. A torch with a potentiometer in the handle lets you taper the current when closing the crater without reaching for the panel, which saves welds on thin stainless steel.
For difficult access take a short cup and a gas lens. The lens straightens the argon stream so you can stick the electrode out further and still see into a corner while keeping the shield. When welding titanium and thin stainless steel, add a glass cup so you can watch the cooling zone.