The most well studied SARM is Ostarine(MK-2866), and that at doses far lower than any bro science suggest is a good dose. LGD4033 has some human studies as well, but once again at a max dose of 3mg a day IIRC, far lower than any "gym supplement" product contains. Even at that dose it suppressed the HPTA considerably. While I have no doubt that they do have an effect, they are very understudied and you will likely be safer and have better effects using a steroid which has many years of use and research behind it. For both blood work is a good idea and both SARMS and oral steroids may be raise liver enzymes.
MK-677 is an interesting one, it not related to the androgen receptor in any way. Its a non peptide ghrelin mimic, which releases growth hormone, and in turn IGF-1. Unlike exogenous GH, it will keep the pulsed nature of GH release. It generally more for healing because it can helps supporting structures like tendons as well. There are other options as well, like GRRP-6 that work roughly the same, but needs to be injected.
The other option to increase GH is via a growth hormone releasing hormone mimic like Sermorelin or the longer acting CJC1295DAC.
The one I would totally stay away from is GW-501516 (Cardarine). Its also not a SARM, but grouped with them. While it does work in increasing endurance, it has no human studies. It has been abandoned because in mice there was no safe dose where it did not raise cancer incidence and tumor size by a considerable amount.
I have not used any of these compounds, but I have read every study on pubmed on RAD140, Ostarine, LGD4033 and MK677. I would really suggest anyone interested in using them do the same. Use sci-hub.tw to grab full studies.