Neither. That's a hairstyle used by Faustina II's daughter, Lucilla. Yours is the middle bronze equivalent of this coin: Lucilla, AD 164-169. Roman orichalcum sestertius, 25.14 g, 31.6 mm, 4 h. Rome, AD 164-166. Obv: LVCILLAE AVG ANTONINI AVG F, bare-headed and draped bust, right. Rev: PIETAS S C, Pietas standing left beside altar. Refs: RIC 1756; BMCRE 1161; Cohen 72; RCV 5505; MIR 16. The hairstyle is clearer in this one:
i looked 100's of coins of Faustina Jr. before i found and got this one, and ironically it was listed as just Faustina..but the bun was a dead give away for me as to who it was..
Wow I thought it was Faustina II after looking at the bun more closely. But I think it is Lucilla now after looking at the picture RC posted Thank you both, April
You might also get confused by Faustina II's daughter-in-law Crispina, who also wore her hair in a bun on the back of her head, but it was larger. See this thread about her hairstyles.