For mild steel, stainless steel, copper and titanium, TIG DC is enough. Aluminium and magnesium alloys need alternating current, so if you weld aluminium, take AC/DC. Choose the current with some margin: for sheet up to 3 mm 160 A is enough, up to 6 mm you need 200 A, above 8 mm and for continuous work count on 250 to 400 A.
Check the minimum current. A machine that goes down to 5 A lets you weld 0.8 mm sheet and thin walled tube without burning through. The upslope and downslope settings and the gas post-flow time decide how the crater looks and whether the weld pool oxidises at the end of the run.
Pulse helps on thin sheet, out of position and on pipe work. On AC/DC machines two parameters matter: the AC frequency, usually 20 to 250 Hz, and the balance, usually 20 to 80 percent. A higher frequency narrows and steadies the arc, a larger negative half-wave portion gives deeper penetration and a narrower cleaning zone.
Match the tungsten electrode to the current and the material. For DC most often WC20 grey or WL15 gold, for AC WL20 blue or WP green. Grind along the axis of the electrode, not across it, because transverse marks scatter the arc.
Above 200 A and on long welds, add a water-cooled torch. In the product listing we state whether the cooler is included, which torch comes in the set and whether there is a foot pedal.