There is a regular shuttle to and from the Disneyland Hotel...in fact there may be more than one. I don't know who the operator(s) is/are, but they are reputable. I know for a fact that if Disneyland has a problem with, or complaints about any shuttle service or taxi service Disneyland bans them from property. I've seen the memo's banning certain shuttle companys from coming on property as well as certain taxi companys or individual drivers. Look for the shuttle that will drop you at the hotel and you should be ok. There are other shuttles which drop at the bus zone (near Harbor Blvd) but the ones to the hotel are monitored more closely for quality as they are more closely associated with the Disneyland Hotel. Hope this helps.
My husband and I always take a Yellow cab from SNA to GCH. It cost's around $32-$34, depending on traffic, and usually takes lees than 30 minutes.
We will never take another shuttle again! The first, and last time we did (Super Shuttle), it took us 90 minutes to get to GCH! We had to wait while others were dropped off, we had a round-trip deal with our package, but we ended up taking Yellow cab on the way back. We just didn't want to go through it in reverse...
Also, even if you do have a group of people with you, Yellow cab does have vans available at SNA... Just a thought.