My thoughts...
I had a throttle body injection (holley projection) on my mustang for a while. Ran pretty good overall. From a drivability/mpg point of view here is my order (worse to best)
1. Carb
2. Throttle body injection
3. Port injection (simultainious)
4. Port injection (batch)
5. Port injection (sequential)
6. Direct injection
My recommendation is if you are going to go fuel injection, go big. Don't just do Throttle body injection (TBI). While you may be able to tune it 'better' than a carb it still suffers from the same basic problem: Wet Manifold. Both a Carb and TBI mix the fuel into the air as it enters the intake manifold. Since the path to each Cyl is a different length and has curves the mixture that reaches the cyl is different for each cyl and will also vary with RPM. They try to design it so the paths are the same as possible and the curves as smooth as possible but in the end they are different. This means you tune to the most lean cyl. Every other cyl is getting 'a little more' fuel. So while you can get some improved drivability with TBI (somewhat depending on the kit, what inputs it has, who tuned it) you still have the wet manifold.
Wet manifolds are not a problem with port injection. The injector is right at the intake port. (Some would argue this is still a 'wet' system compared to direct injection). But you can shoot the exact amount of fuel needed right at the intake and get a much more consistent mixture from cyl to cyl. sequential is the preferred method since it times the fuel shot for each individual cyl.
Of course, our year motors were not designed for port fuel injection. That doesn't mean it won't work but a more modern engine is optimized for port fuel injection. The head design will take into consideration the location of the injector and will, all things being equal, be better than a head/engine that wasn't designed for port fuel injection.
That all being said, if I was going to return to fuel injection I would go port fuel injection and focus on a system that is sequential. The downside is they tend to be expensive, you will not recover the cost in increased mpg.
Also, there are carb setups (webers) that, while wet manifold, are configured in such a way that it is minimized. And the look really cool too..
Anyways, that's my 2 cents. I am not an expert. I have run carbs and Throttle bodies on my Mustangs. I have done a lot of research on this but don't have any hands on experience with port fuel injection on a 71 to 73 mustang.