I have four airbrushes: Badger 100LG (two actually, 1x medium & 1x fine) dual action gravity feed; Badger 150 medium needle dual action siphon feed; Badger 200-20 "Detail" medium needle single action siphon feed; and a Badger 350 Clone single action external mix siphon feed. 90% of the time I use the 100LG medium, and the rest the 200-20 detail. I build cars mostly in 1:24, aircraft in 1:48 and a bit of armor (1:48 & 1:32).
The 100, 150 and 200 all use the same nozzle and air valve, and the 100/150 differs only in the actual body of the airbrush. I could disassemble both, swap all the parts and not tell the difference. The 150/200 use the same color cups or bottles. This gives me parts redundancy. Split the tip on the 200 and I could swap in the one from the 150. In a pinch I could use the 200 needle in the 100, it's just longer in length.
The number one reason I use the 100LG gravity is because it is slightly easier to clean, and wastes slightly less paint. I use the 200 for fine details, as it is simpler to dial in the needle position and lock it in, than it is to modulate the trigger on the dual action brushes. So basically I choose tools which make my job easier.
Ship builders and larger scale benefit from siphon fed airbrushes, but only in that they don't have to add more paint to the color cup, like you sometimes must do with a gravity fed cup. Otherwise, siphon fed brushes don't paint larger surfaces any better. The time spent cleaning the bottle and siphon tube equals or surpasses the time spent adding paint to a color cup.
Badger offers the Universal 360 which combines a smallish color cup with the
ability to rotate the cup to the bottom and attach a siphon bottle. It's likely a fine airbrush, but I tend to dislike tools that try to be different things, as I find they don't do either very well. I'm sure that's not the case with the 360, and is solely my personal preference. I wouldn't buy one because of a preconceived notion.
Since you're a mechanic you'll appreciate how your job is easier by using the right tool for the right job. You won't have just one 9/16" socket, you have both shallow and deep. You won't have just one size of "slot" screwdriver, you'll have various sizes and lengths. Painting and airbrushing is the same. It is better to use a tool designed for the job at hand.
If I were you, and money no object, I would be tempted to get the H&S Infinity 2n1. Consider it the Snap-on of the airbrush world. It will work great, be comfortable in your hand, looks fantastic, and with a big price tag.
But I wouldn't actually get it. I would get the same airbrushes I have (but not the 150, I just don't use it anymore), though I probably would update them to the Renegade Velocity and Sotar 20/20. Consider them the Craftsman equivalent. Works as great, almost as comfortable, and who cares about the looks? I'm more concerned with the money!
I just had a thought and looked at the online Snap-on catalog, they actually offer airbrushes! To my eye they look like Badger airbrushes with a custom handle, except for the single action which looks like the Paasche. They even offer the Universal 360! All with Snap-on prices! Which is why my toolbox is full of Craftsman tools!