As a straight male, after careful consideration I will say... both.
Currently probably SH, but I have high hopes that Karlach will be a cool companion.
There's also a supposed to be a data mined female halfling companion. But, after playing Pathfinder: Kingmaker where you have a halfling companion, Linzi, and they gave her a really cool voice but kinda childish... mmm, yeah kind of a no from me in the romance department.
Actually, thinking about it, I could totally go for a Barcus Wroot romance option
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Yeaah, personally I wouldn't romance him, but I really like him, with just a few interactions available with him he is really well fleshed out.
