Mostly going to come down to personal preference, but some potentially relevant issue on each.
The Taipan likely has the best forward view and also has the highest boost speed (the AX taipan, lacking a utility is the fastest SLF in the game); it's also the hardest to break. Pretty solid thrusters and handles gravity acceptably well.
The Condor will fit places the other SLFs cannot go (it's the only SLF that can fit inside a Thargoid structure without having to fly sideways most of the time), but has the worst vertical thrusters and handles like crap on high-g worlds because of it. It's got the highest non-boost speed and is possibly the fastest over a distance even while boosting.
The GU-97 is the slowest in practice, but has a pretty good view and the best vertical/lateral thrust along with the lowest mass, so handles gravity well.
All the Guardian SLFs fly like slugs and have poor vertical/lateral thrusters, cockpit views aren't bad, but I would categorize them as particularly good either, except that you can see down to a degree (as with the taipan).