In terms of the steel, it really is a matter of personal preference. I have 5x PM2s, and although it is my favorite model, I am definitely not looking to own more. If I end up with a new one, one of these goes - already got rid of three. Although I use all of them, honestly, I would be happy with just my first three.
For me, this is my order of preference,
1) M390 - at this point, my oldest PM2. Used more than any other knife I own. I am familiar with it, with the steel. I know what to expect from use and sharpening.
2) CRUWEAR - hasn't left my pocket since I got it. Wanted this steel for a long time, as I missed the first release. Looking forward to seeing how it compares to M390, granted it is not stainless.
3) M4 - I have this steel in other models, and like it alot. But, it sees less use due to #1 and #2.
4) 52100 - it is a fun steel. Easy to sharpen, fun to patina, durable steel, but again, not too much use anymore. I use my knives for food/snacks, and this one is way too non-stainless for that. Leaves a flavor on fruit and such.
5) MAXAMET - I have my reasons for it being in the last place.