Both are fun. My kids like to take the Monorail. But I don't think there is anything quite like walking down Main Street in the morning. The early morning sights and sounds on Main Street are some of my DL favorites.
I agree with TL67, walking through the tunnel onto Main Street early in the morning is the way to go. Plus if you get there before opening there are lots of characters out on Main Street, and they still frequently do the rope drop which is fun.
If you ride the Monorail, get there early as the platform fills up with early entry guests. Also, I'd ask how many Monorails are running in the morning, if the answer is one....walk, unless you want to wait for 45 minutes to catch a train.
-"Enjoy the rest of your stay here at Disneyland, where all of your dreams come true...well except for two of them, short lines and cheap food."
Honestly I would say the first day to walk and go through the maingate...Theres nothing like walking through those gates, seeing the huge floral mickey and train pulling into the station with all the sights sounds and smells of Disneylands atmosphere...
The rest of your stay do the monorail....Just keep in mind that sometimes there are problems with the Monorail (wont be done with its testing before the park opens, etc..) So to ask the ticket takers...Also there will only be 1 monorail running until Nov 1st so your wait will be 2x long.....When you DO take the monorail for EE, grab a coffee and a bagel and arive atleast 20 minutes early
We just got back from our first stay at DLH & we took the Monorail in & it didn't "feel" right because as others have said you miss walking in the front gate. We did enjoy taking it at the end of the evening or to go back to hotel during the day.