Welcome.
LGD 4033 is the SARM that would really help you out. It’s among the best SARMs for packing mass. Considering you’re skinny, I assume that’s what you need. Ligandrol (LGD) also puts water weight. If that’s fine by you, go for it. But I assume, at your weight/height – it shouldn’t be a problem. It would help you get stronger too.
Then there’s RAD 140 (or if you find RAD 150 which is an updated version) is helpful at hypertrophy (pack on muscle mass). It helps with clean gains. RAD is better for more aesthetic, but then again, I assume you need some water weight too.
Then there’s S4 and S23. While S4 (andarine) is actually good for packing muscle as you hard, it causes dry look with vascularity. S23 too. Both of these suppress your testosterone production – they are powerful. I wouldn’t recommend them to you if you are new to sarms. Many people using S23 and/or S4 add testosterone injection.
All in all, the first 2 seem like a much better option for you.