Cambodia or Vietnam for New year and my girlfriends birthday?

Hi!

I’m currently backpacking in Southeast Asia and planning a 5-week trip through Vietnam. We’ll be in northern Vietnam (Hanoi and nearby) around Christmas, and I’m trying to figure out where to spend New Year’s and my girlfriend’s birthday (January 7th).

Here’s the situation:
- For New Year’s, we’re looking for a lively place with a good backpacker vibe—parties, fireworks, or fun celebrations.
- For her birthday, I want somewhere beautiful and special—relaxed, romantic, ideally near nature or a beach.

Since we’re backpacking, we also want to keep costs in mind, especially flights or expensive routes during the holiday season.

We’re debating two options:
1. Stay in Vietnam until after New Year, celebrate in Hanoi (or somewhere nearby), and then travel to Thailand or Cambodia for her birthday.
2. Leave Vietnam before New Year, head to Cambodia, and celebrate both occasions there (thinking Phnom Penh or Siem Reap for New Year, and maybe Koh Rong for her birthday).
3. Unlikely, but we could get a flight to Bangkok for new year before travelling down to Cambodia for her birthday on the 7th

Would New Year’s in Hanoi be fun, or is it better to move on before the holidays?

Thanks so much for any advice or tips!