I don't have experience but I'll say a Sidewinder because it works with low pressure. Oxygen purity will be best at flows less than the "label" rating of a concentrator, as stated above.
Edit: the chart from GTT is somewhat old. A sweet torch would be the Sidewinder with a Lynx center fire. But I'm thinking your oxygen supply is going to be the biggest limitation for future growth.
https://www.mountainglass.com/GTT-Si...nx-Center-Fire