I've only been to Maui and the Big Island. From my experience, I would vote the Big Island for more to see, quieter, and more snorkeling and turtle opportunities. Maui (Lahaina) was more romantic and better for whale watching.
I'm Heidi, and I'm a stamping addict; Blog
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Friends don't let friends stamp alone! Hudson Valley SBS 3/14/15 - Details coming soon!