Brexit is actually irrelevant to this GE, even though people are trying to make it central. What is paramount is domestic policy; welfare, NHS, education etc. So the answer is 'party' (or whatever voting strategy one usually uses)
I was asked in a recent survey I took part in which was more important to me; the party I support or my view on Brexit. I has to think very hard and decided it was the party.
I have a feeling this will be the swing that puts Mrs May into power so I wondered: Which will be more important to you in the GE; the party you usually support or voting to get the result you desire re the EU?