Here's my honest to goodness take on what is best for actual muscle growth with 1 being best and working down from there.
1) Steroids- test, tren etc. Definitely the can't lose muscle gainer/retainer
2) Sarms- at least s4 as it's what I've tried. It's the only other thing besides steroids that had a noticeable, measurable effect on muscle growth that I could see within a matter of weeks. I used it independently of aas and not part of pct (I was already recovered, so a bit of a difference) and gained about 3-4 lbs of muscle in 5-6 weeks while on a ketogenic diet. When used during pct I don't necessarily gain, but I lose much much less.
3) Slin- I only notice gains with slin when I use it on cycle. Off cycle it doesn't seem to do much of anything. I can't explain that really. When used with steroids it's great. Using humalog pre-workout 3 x a week boosts my gains 25-30% overall. But, again, I don't get anything much from it on its own for some reason.
4) GH- Some gains, but mostly fat loss. But, when compared side by side with gh peptides, GH itself is better for gains when used at 5 iu/day and above. Again, works better with test (what doesn't?).
5) Igf-1 lr3/mgf etc- Insulin like effects. Vague, hard-to-define gains in my experience. Am I getting just the same effects as insulin? Is there hyperplasia? Site growth? If I can't answer that for sure, then I'm not going to rank it up there as very high on my priority list. But, for the insulin like effects alone it's worth it. And, I believe there is some site-enhancement with mgf. But, it's hard to prove. Unlike insulin, I can see some gains when not on aas. So there's that benefit. Who knows what all is going on here.
6) GH peptides- GHRPs, GRFs etc. Great for fat loss, muscle and joint repair and so on. But, without using in conjunction with GH I don't see actual "gains" from these combos. Throw in a bit of GH in the mix and the effects double, joints feel better, weight is gained, muscles fuller. Greatly synergistic together. Also, since they help keep you leaner, there's the benefit of being able to take in more calories and not having them go to fat. Theoretically more will be used for muscle. But, on their own, I think most of these peptides even have kind of an anorectic effect and even cause more bowel movements. Valuable, but you gotta work to make them work for you with proper diet etc. Not a magic growth bullet like testosterone is.