I’d advise to use a full-brain image with the best resolution available. If you have a highres full brain T2, maybe use this one since it shows the STN. Planes don’t really matter, it should be as high-res in all dimensions as possible (I guess an optimal file could e.g. be a 1x1x1mm T2 or T1).
If you use a T1, please name it anat_t1.nii in order that Lead-DBS uses the T1-MNI template for normalizations (this only works with ANTs).
dcm2nii is the optimal choice, please export the files in 4D nifti format (.nii ending).