I have used both the Firepod and Firebox, but not the Saffire. However, I have used a number of Focusrite Pre's (Platinums and ISA's). (I generally worry about the pre's before the A/D conversion. Both are important, but it starts at the pre.)
In their class ($), I would describe the Focusrite pre's as being warmer, smoother and more open and pleasant over the Presonus units. Definitely more "colored" with the typical British twist. (A good sound in my opinion) I think they are about the best pre's you can get for that price, but that is all personal preference of course. (Remember, we're not talking John Hardy, Great River or other high end pre's here.) Since the green pre's (which the Saffires supposedly use) are supposedly somewhere between the Platinum and ISA series (Greens were out before the Platinums came out), they should be pretty decent, especially at that price. I can't say anything about their A/D-D/A conversion though since I haven't used their Saffires. Focusrite pre's are high quality in their appropriate price ranges.
The Firepod is clean. However, was a problem with my Fireboxes that I tried to work through with Presonus but they could not answer what the problem was. They sort of threw up their hands after a few days and basically inferred that the Firebox is good enough at its price range for its intended purpose and market. (To which I must agree.) After using a Firepod for about a year or so and noticed something was different. I tried 2 different Fireboxes and found that some very narrow harmonics begin to appear at about 6 KHz. These harmonics show up as very narrow bandwidth spikes every 1KHz, so you see them at 6, 7, 8, 9...18KHz. There were also some issues with power supply induced harmonics (60 & especially 120 Hz), which something better than a wall wart power supply would clean up. Oddly, the Firepod showed none of these problems, not even the power supply issue. Now the level of these signals is very low, but a few were as high as -50db.
(All of this was confirmed with a high dollar FFT analyser set-up) They are additive to the input signal however, so they will take off a half a db or so of your headroom at the top end (it will be VERY, VERY minimal), but are generally hid in the grass. You will never notice the high frequency harmonics audibly, unless you have a very high end monitor and are recording very quiet sources. Even then, you may be hard pressed to notice. If you're rockin', it will never be an issue. You may notice the power supply harmonics however. I expect that the high frequency harmonics problem is something strange with the A/D conversion, as harmonics problems with the preamp should show up as mathematical multiples, not every 1 KHz. (Perhaps I had a problem with a specific batch of Fireboxes, as they did come from the same source at the same time.) I eventually returned the Firebox. With that said, I personally would probably only consider the Firepod, not the Firebox.
If it were me, I would buy both the Saffire (any flavor) and a Firepod from someone with a liberal return policy and give them both a run for a couple of weeks. Let your ears make the call.