We are flying into Orange County Airport on Monday.
Which is better, Disneyland Express or Super Shuttle. Do I need to book online or just wait until I get there?

So do they drop off at all the hotels? We aren't staying on Harbor (Peacock Suites) so we are a little off the main drag. Is there only 1 shuttle or do you need a schedule of some kind?
I think I read a taxi is only about $35 from Orange County Airport. To me, that would definitely be worth it to not have to wait for other stops and for the shuttle/bus to fill.
When I was there in October, the taxi flat rate was $45, but only if you called ahead. If not, there was no flat rate which made it about $48 for us since we had no reservation. If you got stuck in traffic, that amount would be higher. I suspect if you demanded a flat rate, someone would give it to you, though.
For fewer than 5 people, I'd use Super Shuttle (actually, I might use them anyway). It's cheap! Here is a good coupon code that will get you $3 off each direction: UYR59 I believe most other coupon codes give you $2 off each way. One note: they stopped giving the discount to every member of the party on the same booking, so book each person separately to get the full $6 off roundtrip pp. That makes the fare $7 each way. You have to book online for that deal but then you can add in the tip, which I always do, and everything's taken care of.