Efficiency is important. I believe max out the armor first would be a great idea.
After Misty Marsh, there are Roc and further stronger enemies with higher attack, you may need to max out your 3 armors to help you go further.
I do not mean to let you stop at Misty Marsh, you can keep exploring areas, but spend some time on farming snakeskin and upgrade your armor, so that you will feel easier to pass next area.