I've only heard the RS1 briefly so I'll just comment on the 225(i). The HF2 one is definitely a warmer headphone compared to the 225. The bass on the HF2 has much more impact. Some of that might be a mid bass hump, but it doesn't really intrude on the mids. I think with the richer mids the HF2 is more balanced than the 225. I'm not pretending the HF2 is a balanced headphone or loses the Grado family sound, I'm just saying, to me, it's a bit more balanced. The HF2 is quite a bit more refined overall also. The highs aren't as aggressive (harsh?). The HF2 is truly a great Grado. I often miss them. They also improved (mainly soundstage) with the jumbo pads, IMHO, where other Grados did not or made the sound worse.
So why did you give them up?
I like the MS2i's but I think I preferred the 225 and I've been told that the HF2's are very similar in signature to the 225's just with better bass and mids. If I have a criticism of these MS2i's it's that they dont have as much bass impact as I wish they did, but they are silky smooth and synergize well with a good deal of my library. So if I opt to go to the HF2 it will be to satisfy my desire for more bass impact but does that then mean I have to compromise on something else?
The other thing is spending $200 for a pair of new 225's or a used pair of MS2i's is quite a bit different than dropping twice that amount for a pair that's probably similar to both in many ways. Although I see from your sig that you were willing to spend even more than that. Which is why I suppose you gave them up. Do those things sound as sweet as they look. And if you find yourself missing the HF2's is it because you get a lot of bang for your buck?