IGF-LR3 is going to cause for faster effects and site specific growth, but has a much more specific dosing protocol. PEG-MGF is slower and not site specific. There's a reason why IGF-LR3 has damn near doubled in price over the past few months, and that is that it has a very high demand for it.
A lot of people will use LR3 on workout days, and PEG-MGF on off days.
I might also add that PEG-MGF is usually done subq as opposed to IM.