Where would you prefer to spend four to five days? Too different to make a fair comparison? Focus: good food, nature, hiking, massages, exploring historical sites and temples. Shopping is a plus, but not a deal-breaker. Have wonderful beaches in Hawaii, so beach resorts are not important to me. Expect I'll eventually do both, and am leaning towards seeing Chiang Mai first.

No question -- chaing mai. It has everything you want.

any place but chiang mai

They are very different destinations. I'm not fond of Chiang Mai. If you've read other posts of mine, you'll have heard that already. I loved Penang. However, we stayed right in Georgetown at the E&O and were there for the cultural/historic sights as well as for the great hawker food. There are beaches in Penang (which is a large area) and I would not go there for the beaches. We spent five days six nights in Penang, and it was the right amout of time for us. We spent 4 or 5 nights in Chiang Mai because of Royal Flora. Had Royal Flora not been going on I would have died of boredom just in CM for that period of time. So if you want to spend 4 or 5 days there, you'll want some out of town trips. Note tht CM is a huge, sprawling city with no public transportation. You'll need a car and driver if you plan to do any shopping, for instance.
If you stay in Georgetown, you'll walk and use rickshaws and an occassional taxi.

Kathie and I have to agree to disagree about Chiang Mai. Yes, the modern city is a big sprawling affair, but for a tourist, the things you might want to see are mostly contained in a small area that can easily be explored on foot over the course of a few days. The old city is full of temples, museums, galleries and shops, while the river area has the night bazaar, a couple of fascinating fresh markets, and the Charoen Rat Road gallery/dining area.

If you're there over a weekend, there are the walking streets on Saturday (Wualai Road) and Sunday (Ratchadamnoen Road). When you get bored of the city, you can escape to the Mae Sa valley for some walks or elephant rides, and there is even white-water rafting nearby. I've visited Chiang Mai more than 20 times, and I'm never bored.

That said, I am equally fascinated by Penang. But for "nature, hiking, massages" in particular, I'd give the nod to Chiang Mai.

Michael, you are in good company. Several people whose opinions I respect, including Glorialf love Chiang Mai.

Considering that you're interested in massages, nature, hiking etc, would say Chiang Mai...

Thanks for the additional comments.

Yes, I had expected to take several day trips out of CM.