Heres how it goes from my point of view:
1- If you are on a bit of a tight budget as in hotel wise and still want to stay on Disneyland Property, you have no kids, or if you do and they are older and dont need much to keep them busy other than a pool and a TV while at the hotel l would say it should'nt be a problem staying at the Paradise Pier Hotel, its perfect for that situation.
2- If you've got kids of all ages who just love the great outdoors mixed with Disney Magic or just something cool and new I would say give the Grand Californian Hotel a shot, its spectacular, it has its own entrance into Disney's California Adventure Park and has a side entrance right in Downtown Disney....which is a great plus for teens and kids of all ages.
3- If you really want to make your Disneyland Resort trip the best it can be stay at the gem of all the hotels, the Disneyland Hotel. It has something for everyone of all ages and for everyone of all tastes. It has the biggest grounds of all 3 hotels and has the most to do of all the hotels. Its got great views of the parks and is right at the end of Downtown Disney, so you have everything right in front of you. It is a bit of a walk further to the parks than the Grand Californian but it is quite worth it, trust me.
My Personal favorite is the Disneyland Hotel, it was Walts Hotel, he put his magic touch into it and you can still feel it all around you and even when your not actually "in" Disneyland park you still feel as if you never left the park since the hotel is so Magicaly themed.
Hopefully that helped just a tad bit.
