None of them will be as important as the connections that don't exist on any macbook yet.
ie USB3, Light Peak, ESata.
I am really unsure of why Target disk mode is that useful, I've never really had the urge to use my macbook pro as an external firewire drive on another computer. Also apple is working on target disk mode via ESata as I recall.
http://arstechnica.com/apple/news/2008/08/apple-aims-to-patent-target-disk-mode-for-esata.ars
Esata is the port I want, the combined usb/Esata port would have been great. Quite a few pcs and notebooks have this port so I don't think it's due to technical issues.
And yes, Esata is Faster than firewire. 3gbs vs 800mbs. And ESata might get bumped to 6gbs soon tooNow this is all theoretical unless you have an internal /external higher spec SSD. But in practical use at work, I know that a firewire 800 linked HD is slower than an internal Sata Drive of the same spec.
You forgot Firewire 3200: a 3.2Gbps interface, and since firewire is peer-to-peer the actual throughput is approximately 98% or 3.1Gbps. USB3 is a 4.8Gbps interface with an actual throughput of approximately 47% or 2.3Gbps.
So, yes, I'd rather have firewire on my Macs.