Use them consistently. It makes your writing more betterer.
Consistency comes in as many flavors as different spellings for the same word and all variations of correctly punctuating the same sentence. Rules is rules. Adhering to them establishes credibility. Breaking them is okay if done consistently and to make a point. We call such consistency in writing style. Excellent writers have a style, call it a voice, identifiable as their own even though that voice follows rules the writer would rather not. Competent editors and publishers see to it. Compromise happens, sometimes. It’s a process. It’s credible and/or creditable. But go with one or the other. Make sure a word means what you want it to mean, and be consistent.