Is there a middle way between working towards personal liberation and liberation for all sentient beings?

Dhammapada verse 166

For the sake of another's benefit, however great it may be, do not neglect one's own (moral) benefit. Clearly perceiving one's own benefit one should make every effort to attain it.

My own approach is to help others, but when it's not possible, or if such help, though well intentioned will not be effective, and worse, if it will harm me (morally), then I choose personal liberation. It's a case by case thing, no single answer for all situations. Compassion towards all should mean compassion towards oneself too. To not be captured by either extreme is the essence of Buddhist wisdom.

The whole of Buddhism is the middle way. Initially, when someone is introduced to Buddhist ideas it can be explained in stark contrasts to help the learner understand. As learning matures though one must learn to deftly weigh the situation and choose the teaching appropriately.

The middle way teaching is to cut through this morass of opposites. The middle way is not the half point, or doing things in half measure, or being confused.

See Dharma talk by Thích Nhất Hạnh on the Sutra on the Middle way Part 1 | Part 2

The middle way is not a simplistic teaching, it is not mere common sense. It is perhaps the most sophisticated of Buddha's teachings, requiring a working understanding of both emptiness and dependant origination. In the above talk Thầy Nhất Hạnh so eloquently teaches it, do read it.

It depends on what you or your school has decided about the nature of who we really are. If we are so throughly interconnected, interdepedent, either in a Huayen way or maybe just as one big shared soul, (albeit a changeable, mortal one) then the relevant unit for liberation is all of us. Either we all make it to the other side or none of us do.

The middle way applied outside of it's original domain, debauchery vs asceticism, can lead to some weird results. The sum divided by two of any pair of actions that are opposing on some scale isn't necessarily going to be the point of wisdom or even coherent. Should I take a girlfriend? Well, how about for 1/2 the time. Or 1/2 a girlfriend. Shall I buy a car? Well, I'll buy 1/2 car.

(Mahayana thinking in general are often at danger of this, especially when applying sunyata/emptiness to things outside of its original domain-- the investigation of experience.)

The logic of the Bodhisattva vow leads people towards various theories of univeralism. The Lotus Sutra is a good example, where it is posited that the other two paths (arhat and pratyekabuddha) are illusory, rest areas on the way to full Buddhahood.

In the Lotus Sutra, and other Mahayana systems, the difficulty level of achieving full Buddhahood declined, where it sufficied to have faith in the Lotus Sutra, or where it sufficed to do nothing at all and rely on Amida's vow, and in many text I read, I feel like it is saying that vows and bodhicitta are like lighting the fuse on dynamite, once it is started, it creates an inevitable chain reaction. So the task of the Bodhisattva is to light these fuses more than to work on each step of everone's enlightenment. (That said, in both the Brahma Net Sutra, Avatamsaka, etc, the lay and monastic bodhisattva is expected to above all teach as the primary way of helping others reach the other side.)

There is no conflict, the dichotomy is false and is based on incorrect understanding. As Buddha said in Sedaka Sutta:

When watching after yourself, you watch after others. When watching after others, you watch after yourself.

And how do you watch after others when watching after yourself? Through cultivating, through developing, through pursuing. This is how you watch after others when watching after yourself.

"And how do you watch after yourself when watching after others? Through endurance, through harmlessness, through a mind of goodwill, & through sympathy. This is how you watch after yourself when watching after others.