Should I take the Mercenary option?

It depends what you want from the season. Mercenary trades a bit of control for gold:

Take Mercenary if:

• Gold (a permanent currency, never reset) interests you more than your specific camp
• You don't care which faction you play (it changes every Reign anyway)
• You just want to start fast without thinking about placement

Avoid Mercenary if:

• You care about coordinating your placement with your alliance (even though the faction choice is never fully guaranteed)
• You'd rather try to aim for a specific camp

Key reminder: whatever you choose, your alliance follows you and remains your real group. The faction is temporary. So Mercenary is rarely a bad calculation: you gain permanent gold for accepting a placement that's temporary anyway. For many players, it's a small free bonus.