I'll put some insight in.
My first rig I got when I was young, simple crate 10W practice amp. A couple years after I got a BOSS MT-2 metal zone pedal, which was a fun novelty at the time. The issue with the MT-2 is that if you don't know what you are doing with the EQ, the tone you get will sound pretty fizzy. Anyhow, I was into punk at the time, so tone really didn't matter to me that much.
Then junior year of college, a friend sold me a 1991 Marshall JCM 800 and a Carvin 4X12 cab with V30s in it. At this time, I was just starting to get into metal, with my main influences being Thrice's Artist in the Ambulance, and then later Atreyu's The Curse. I could get Thrice's tone pretty good, but for a true metal tone... not so much.
This rig was pretty good, but the issue with Marshalls, especially the older ones, is that if you are going for a metal tone, they don't sound good AT ALL at low volumes. You have to buy a boost pedal, or as I did, use the BOSS MT-2 for the distortion. I quickly realized that this was an issue, because I didn't want the MT-2s fizzy tone for metal, and I needed it if I was going to go through the Marshall.
So I was looking for an amp that had a great distortion, the kind that feels like it is moving your chest as you hold out a chord. I also wanted a good clean channel and a good amount of versatility. I didn't want anything quite as thin as the 5150, because while those are great rhythm amps, they felt a little to dry for leads.
I tried a double and triple rectifier, but they all felt too muddy on the low end.
This is when I found the ENGL powerball. I gotta say I love this amp. It gets you those Nevermore tones easily, and can go from a bell like bottom end to a thick, crunchy bottom end. Some people complain that it is too compressed, but I have found that if you keep the distortion at or under half way, you still get a brutal attack but you can hear chords very well and there is a good amount of dynamics. The lead II channel thickens the tone up quite a bit, and is awesome for solo tones.
Then, it was time to tackle effects. It never made sense to me to go the pedal route, because you would need so many pedals. For example, if you wanted to have two different speeds of delay on in two different parts of a song, you have to buy two pedals. Also, the "tap dancing" idea of switching 2-3 effects AND my amp head was not an option, because the band I was in went very quickly from rhythm to lead work. I wanted a one button, switch all rig, which is very, very expensive if you want to work with pedals.
That is why I went for a rack effects unit. I got the GMajor 2, and it does a majority of the stuff on it pretty well. It has compressors, delay, reverb, harmonizers, chorus, a noise gate, and much more. The thing I liked about it the most was it has stereo relay switches. That means you can program the switch open or closed in your patch, and it will do analog amp switching as well as effect switching, all via a MIDI controller. Gone are the days of hitting multiple pedals to go into a lead! Now I hit one pedal, and I go from Lead I on my amp (rhythm tone), to Lead II with delay, reverb, and chorus. That is a great luxury for fast metal performances!
I am thinking about getting an Axe-fx, but I am really happy with my rig overall, so I am still undecided on that.
Hope that helps!