You'll get range of answers as big as the price range! But I will try to give you my opinion.
I'm a hobby guy too. I wanted AC as well as DC to allow doing aluminum. I started with a Chinese import, it got me started into TIG. I currently have a Miller Dynasty 200DX. It was expensive but I was lucky enough to come into some unexpected money so I got it. I worry about the day my Miller goes beyond repair so I keep shopping from time to time to see what's out there.
There's a ton of Chinese imports that are less expensive. A lot of them don't have brick and mortar store front. Those brands to me are problematic in that any kind of service if you're lucky enough to get it the shipping is on you both ways. A buddy of mine has an AHP, I've tried it and was impressed but he has had to have it serviced. They were good about helping trouble shoot it but he ended up up shipping to get service there and back.
We have a store here called Harbor Freight. They sell cheap imported tools. Some of it's not so good but a lot of the products are decent. They have recently added a store brand line of welders including a TIG model. One of the managers told me they hired an ex Lincoln engineer that is responsible for the design. It's priced around $1,000 dollars and has a one year warranty that can be upgraded to 3. It's not as full featured as the Miller but it's got a lot and I think would be a choice if I'm ever looking for a new welder. I especially like that I could take it back to a store that's 10 minutes away if there is ever any issue during warranty.
There are also some good midrange priced brands like Thermal Dynamics and ESAB. I have no experience with them but a lot of people seem to like them.
I'd look for a brand that has a local store front. If you want to do aluminum AC is a must. AC balance control is next and AC frequency is a nice to have but not as essential as balance control. Pulse is awesome for anything less than 1.5mm thick. 200 amps is more than enough to do any motorcycle frame work. I wouldn't get too worried about duty cycle, if it's high great, if not it's not a big deal unless you are in a production setting. The Miller has the ability to chose a variety of AC wave forms but that's not essential either unless you are going to weld less than 1mm thick or happen to be used to an old inverter machine. Make sure the torch connections follow an industry standard for connections so you can upgrade the torch and cables. Air cooled torches are okay for getting started but if you get serious you'll want a liquid cooled torch. You can run a liquid cooled torch all day and they are much smaller than air cooled torches. CK Superflex cables and torches are expensive but worth every penny. I always get flex head torches and Superflex cables. Nothing worse than fighting a stiff heavy cable in an awkward position. Most welders come with a foot control and at least have the connections for power control on the torch. Foot control is essential and the best way to start. There are several formats for torch controls. I don't use it often but occasionally you find yourself on you back or you belly and then some kind of torch control is essential.
Good luck!