It's a great dilemma. I can't remember seeing anyone unhappy with either service. I'm a longtime Smugmugger, but I've never looked seriously at Zenfolio, so I can't compare.
Here is a list of things I like and dislike about Smugmug from an
earlier post:
Things I like about Smugmug:
1) Unlimited storage and bandwidth - I have over 10 gig of photos stored there.
2) Easy uploading - there are several uploaders, including ones that allow you to just drag and drop pictures or folders. You can also upload directly from Lightroom.
3) Easy backups - You can order a backup disk from them. There are also free utilities that will allow you to point to one of your galleries and it will download all of the photos for you.
4) Good privacy control - You can secure or hide galleries or pictures.
5) You can allow people to download the original size pictures if you want, but the pictures are also available for viewing at many other resolutions.
6) Video - You can upload videos and view them. They look much, much, much nicer than
YouTube (see my latest attempt at video
here). You can even post 1280x720 HD videos with a Pro account.
7) Good tools for organizing, re-arranging, and managing your photos.
8) An iphone interface that works well on other PDA's (like my Blackberry) for when you want to show someone a picture while away from home.
9) Traffic tracking so that you can see what photos people are looking at.
10) Communities - for sharing photos on similar topics (like the
Disney) community.
11) RSS feeds so that someone (like Grandma and Grandpa) can subscribe to your photos without you having to notify them when you've posted new ones.
12) Link to Google Maps for seeing your photos mapped
13) Pricing control - so you can set the price for prints by gallery.
14) Pre-print proofing - so you can let your customers pick the pictures they want, then tweak them before they are sent to the printer.
15) Control over Google indexing - Let it find some pictures and prevent it from finding others.
16) Incredible support - they read and answer e-mails. They have a resident pro that will gladly offer you advice.
17) Their own
forum dedicated to photography in general as well as their site in particular.
18) It's obviously owned and run by people that truly love photography and technology. It's a great combination.
Here is a great article on the company.
19) Constantly improving - I've been with them for several years and the site has seen steady improvements in their interface, performance, and offerings.
20) Customization - They let you do a tremendous amount of customizing of your pages. That's one of my goals for 2008.
What I don't like about Smugmug:
1) They deal only with sRGB images. They can't print Adobe RGB. It's one reason that I do my own printing at home rather than ordering from them.
2) They don't embed EXIF data in the resized JPG images. You can only see the EXIF by visiting the site or by looking at the original image.
I can't comment meaningfully on the quality of the print services that they use and don't use. I've never actually seen a print from them. People that have printed my photos have told me that they are very happy with the print quality, but the fact that they are printing my photos shows that they aren't all that particular.