Except for Pathfinder, those are all less popular than D&D, so I doubt you can find anyone who has played all of those.
I'm a bit familiar with Trailblazer. It put a little 4e into 3e. As I mostly DM, I didn't bother to look at the class mechanics, which might be the part you're mainly interested in. (The class changes are bolted onto what's in the SRD rather than being their own thing. That's both a feature and a bug.) Instead, I was interested in monster rules. Trailblazer has "elite" and "solo" templates that are obviously 4e-influenced and look like they work pretty well.
Pathfinder has lots of little changes. The most positive change, IMO, is to low-level wizards and clerics. Most wizard subclasses have spell-like abilities that are more powerful than cantrips but weaker than 1st-level spells, and can be used 3 + Int times per day. Even universalists get something. Alas, they vary wildly in terms of usefulness; more options can mean more
bad options. Some, such as the necromancer's ability, aren't really worth the paper they're printed on. I really liked the conjurer and fire wizard spell-like abilities though. Admittedly these abilities lose their luster as the wizard gains levels, but ... you're now a high-level wizard, you don't need more power, you probably should have less
Cleric domains often have spell-like abilities as well. Handy if you're not a "meaty" cleric.
Pathfinder cantrips are also at-will. They're still really weak, of course, but if you don't want your wizard to ever use a bow, you don't have to.
Iron Heroes is starkly different. In hindsight, it has a little 4e in 3e, much like Book of Nine Swords. It has "reserve points" that work kind of like healing surges. (In 4e, the number of hit points a PC has at any one time is pretty limited, but the amount you have over the course of the day is pretty high.) I don't recall there being in-combat healing magic in it at all. The classes tried various methods to make martial combat interesting. There's also a weaker wizard class, a bit like the late 3.5 "weaker" caster classes such as Beguilder, Warlock, Warmage, etc. There were some vague rules (or maybe I just vaguely remember those rules) for weakening monsters that required magic to deal with. I think it had a Bestiary as well, which is probably a better way of handling things.
Is E6 even a house rule? If the DM says they will end the game before 7th-level, that's not really a house rule, that's a campaign reaching its natural conclusion.