pros and cons

Cost. I don't have the exact numbers in front of me, but its somewhere. I don't know which is the cheapest/most expensive, but one difference is the cost. You can email someone at CalGreeks, or just ask individual chapter's Financial Chairs. This is probably the tie-breaker.

Location: Theta is closest to Campus, DDD and GPhi are about the same. GPhi is on the row, DDD isn't, but still in an okay location/close to I-house/Coffee.

Sisterhood/Reputation: All pretty similar. All three have strong sisterhoods/good big-little weeks. They all party about the same amount. DDD used to have more partiers, This isn't the case anymore. All have exchanges/invites that girls can go to.

Physical House: According to Cal Greeks, DDD has 28 rooms, GPhi has 37 rooms, and Theta has 33 rooms. GPhi has a huge backyard, Theta has a Gym, DDD has a good view. This comes down to personal preference during recruitment. Where do you see yourself living/hanging out?

Honestly, they're not too different. They'll give you similar experiences. Go to all 3 if you can and meet their girls. If you can't make it, email their recruitment chairs and ask about other COB events/invitations/etc.