The best steroid for bulking is the one that provides the most muscle at the same time, not causing noticeable side effects.
It is straightforward to find steroids that can achieve high weight gain, but this effect has its price. For example, steroids like Dianabol cause a lot of water retention and thus create substantial increases in body weight, but it also causes gyno (development of female breast tissue). Another example might be Trenbolone. This compound provides incredible strength and mass building effect; however, it also suppresses natural Testosterone production significantly (it does actually by itself act as an Anti-Catabolic if given in high doses) and will make you much more susceptible to injuries – especially joints since Trenbolone already by itself can cause a lot of joint pain.
This, however, doesn’t say that any steroid will make you look like a bloated balloon. If you combine anabolic steroids with some other compounds, if they are used in the right way and the right stack, there might be results that do not come close to Dianabol or Trenbolone, but they will be much more safe and sustainable. For example, Anavar has been shown to provide similar effects as Dianabol in strength and weight gain, but without most of the side effects (no water retention, no gyno). Also, Oxandrolone is very helpful when achieving maximal gains with low side effects and minimal suppression during bulking phases. You could even consider taking a combination of Dianabol and Oxandrolone since they have a different mode of action and thus complement each other.
Don’t forget that steroids are combined with a proper diet for the best results. You can’t gain muscle by taking supplements without adequate nutrition – this will only lead to poor quality muscle tissue, which won’t be as hard as you might expect.
In conclusion, I would not say there is one general best steroid for bulking, but it’s possible to achieve significant gains without discomfort if you pick your compounds wisely. If anything, I would say Anavar/Oxandrolone + Stanozolol (Winstrol) or Primobolan with some testosterone (if you want to have fast gains) are the most beginner-friendly stack. Of course, if you are more advanced and know how to combine steroids, do your research before trying anything out.