For Biotic builds, I prefer the Fusion Mod of Rapid Deployment.
This mod increases Recharge speed of all powers by 50% and puts a 30% penalty on Weapon Damage. The nice thing here is it's not restricted to just biotics, it's all powers. So if later down the road you decide to swap in a tech or combat power, it still works.
You can take the cryo pod perk that reduces the penalty by half giving you a 50% recharge increase and only a 15% decrease in weapon power. If you're using a Biotic build, you are likely not using your weapon that much anyway, and most Biotics use high damage shotguns that honestly don't seem to be effected much by a 15% decrease. This mod is obtained by activating the vault on Kaadara.
Another good one is the Fusion Mod of Biotic Mastery which gives you a 30% boost to biotic damage with the cost of 20% reduction in all other damage. I don't like this one as much because I prefer the recharge speed bonus of the previous mod, but this is still a good way to go. This mod is earned by defeating the Architect on Eos.
The Fusion Mod of Adrenaline is a good mod, but in my opinon is situational. Most time you'll be rapidly racking up kills, but as said before in fights with larger enemies, this mod can be a serious draw back. In the end, it's up to you.. there is no such thing as the 'best mod' or the 'worst mod,' it just depends on your build and play style.