If you have the room and the power abilities, you will not be disappointed with a Miller Dial arc HF or a Miller Syncrowave, with the latter having Squarewave technology, which is better than straight waveform.
A Miller Dynasty would be the cats meow. The new inverter stuff, I hear is awesome but I grew up with transformer welders and will die with them.
Too old to learn all them buttons.
I now have a Miller Dynasty 280DX. It is a great welder, 13 years I've had it I believe. A steel TIG does not need the features an aluminum TIG needs. You might use an air cooled torch for steel, You pretty much need a water cooler & water cooled torch for aluminum welding. I did weld aluminum with a Dialarc 250HF. The sine wave fixed at 60 HZ is not ideal for aluminum, you'll love a transformer for steel. Transformer based welders are very power hungry, while inverter based use half the input power. Some worry about all the electronics in an inverter welder being undependable.
If you want to also be able to weld aluminum, look for:
High ampere output.
High duty cycle. Most are rated with duty cycle at less than full output, a 300 amp peak welder might have a 60 % duty cycle at 200 amps. Look for the best duty cycle.
I want square wave supply, with adjustable balance. Aluminum is mostly welded with AC power. Sine wave power dies twice per cycle, 60 cycle dies 120 times per second. Shielding gas is a poor conductor, it must be ionized to be more conductive. Electrons are concentrated in the Electrode Negative half cycle. They are very effective at ionizing the gas. Electrode Positive half cycle, electrons are less concentrated on the greater surface of a workpiece, less effective at ionization. Square wave, the current never dies, it only changes direction, ionization isn't lost. HF, an overrunning High Frequency at high voltage / low current helps to maintain ionization.
Adjustable frequency is a nice feature. High frequency narrows the arc cone, low frequency gives more penetration.
