Front or rear shackles work equally well. Front or rear steer also works, and depends on your choice of steering box, and location. Both of mine are front steering boxes so they steer off the front side. The Auatin is rear shackles because that was what it originally had, and it worked out to keep it. Falcon is front shackles, as that's what I usually choose on most of the axles I've done when I had the choice. I try to always put the tierod in the rear, as that's the best, and keeps it protected from possible damage, but the Austin also went with tierod up front, and drives nice.
By "fixed spring" are you referring to a transverse spring? Of course you can't do parallel springs with fixed mounting on both ends, and transverse springs are a real challenge with larger/heavier cars. I'd have no prblem with transverse spring setups on smaller or lighter cars, and they look very cool! On big cars it's tough to get a wide axle and all that weight, and still control body roll with a transverse spring setup. Saw a '68 GTO running one at the Nostalgia drags last year, and going 170 mph with it. Talked to the owner and looked it over up close in the pits. He was running air shocks at each end to stabilize it, as he said the original coilovers wouldn't keep it straight on the top end when racing. Can't imagine what turning would have been like at 70 mph, or lane changes/ruts!