I think marine, nature, and time work the best with beasts.
Marine can get you teleporting into the middle of the pack to grab aggro (if you like bodyguard mode) and everyone being melee means they're also clumped up for the cone heal for easy repositioning on yourself. With them all being melee, it also makes it easy to fire off your aoe buffs without worrying if one or two henchmen are outside the radius. Shifting tides being anchored on a henchman is also nice since you know they will be in melee range. Then the fact that marine gives a bit of defense, resist, absorb, and heal means you can keep them alive very easy while also giving them a nice amount of added damage. And brine is great on big targets, which your single target beasts will already be good at dealing with. The only issue is you'll want pretty much every power, so you'll have to be picky on pool powers. I think this is the most fun (obviously opinions will vary) set of these three.
Nature keeps you alive. Not a ton of added offense until your T9, but the aoe hold is great for single target henchmen, since it will make the minions and some LTs a non issue. Heals, absorb, resists, more heals. Your beasts should be set here. Like Marine, it's got a cone heal which takes some getting used to, but all melee makes it easier to position for. There's a bit of -regen for big targets, but nothing insane (I think it has less -regen than standard long recharge ones, but I don't have access to mids right now to confirm). And the toggle debuff is always nice for a corner pull when solo or in small 2-3 person groups. Definitely the most thematic of the three sets here.
Time will easily cap your beasts' defense, but it sorta locks you in to mace mastery for the power boost. A toggle debuff anchored on yourself means you'll be in the fray with the beasts, and the aoe heal is very powerful, and the heal over time effect makes it so you don't "waste" the heal on allies near full health already. Both of those being PBAoE synergizes well with beasts being melee again. You can also use distortion field and your single target hold to stack holds on bosses for a few seconds, and the +chance for hold proc in each can make it much more consistent. Unfortunately, time's +recharge buffs don't do anything for the beasts, but they do benefit from the recovery, regen, and damage buffs from the +rech powers you have. But the recharge helps you, and you can get pack mentality and pack fortification going more smoothly with that recharge. I think of these three sets, time is the most straightforward to play and slot, but maybe the most boring, which also means you have time to throw in a personal attack or two without much sacrifice.
I'll throw an honorable mention to traps, as it's very solid, but on big teams you'll have to cycle through your powers on a group to group basis, since competent, fast moving teams will clear a group before you're able to set another mortar or launch seeker drones. OH! Seeker drones. Beasts don't get a 4th pet power for unique invention slots, (no gang war/hell on earth style summon) but seeker drones can take them, which may ease some slotting issues, as pet slotting on mm is always a bit of sacrificing one thing for another. If you want to solo, traps is great, and on teams it's just going to feel like you're contributing a little bit less, unless the team is barely staying alive.