Don't know about flights out of Boston but for business class, United has 1-2-1 layout so everyone has access to the aisle.

LH seems to be mostly 2-2-2 layout and has older lie flat seats.

But many people prefer the food and service on LH more.

If the OP does think he or she will try to qualify for status, then a UA flight might make more sense than an LH flight.