I'd take some of both. Brody fitted into newborn really well, but at 5 weeks they started getting too wee for his legs. He is now in 0-3 months. I'd def have more 0-3 month clothes than newborn.
I also really recommend just getting babygrows and vest tops for underneath. I bought lots of outfits, but I can't be fussed with them and change his clothes a lot. Babygrows are easy!
xx