like Maria I do both.
besides EMH, DME, disney transportation in general, delivery your purchases, being able to charge your purchase with your room key, haven't your tickets on your room key - the big difference is the CM. On site they will generally go the extra mile for you. Not a problem and will try their best to please you.
offsite - varies - greatly. Now the ones at CWR were great. they really, really try to make you happy. even with a language problem that didn't stop them.
with VV - the front desk was great - but the rest of the staff. I say good morning no matter where I am - the looks I got from their staff - say it all. Plus there was somebody in the entrance way in each building to help you - but he was only interested in selling to you.
I found the maintence, front desk, life guards at VV to be excellent but the rest of the staff needs to learn about customer relations.
at other places it can be worst - one hotel I checked into the person who gave me a room was so high (drugs) that the next morning they didn't know I had checked in....
when you stay offsite you might have a wonderful experience or awful - alot depends upon the staff. Some places try their best even when they are small and don't have the stuff of a bigger place. Other places don't care at all.... I try to avoid these....
every person experience is different - because every person is different. what I love you might hate.
Try offsite - you might love it and never want to stay onsite again. Or you might say what did I get my self into.... I wish every trip to Disney was great, carefree, and the best trip of a lifetime - but they aren't.
or you can be like alot of us and start doing both offsite and onsite. you get the best of both worlds.
I like to stay (this year) on site for Sun - the MK EMH nights is Sunday. So I will try to stay onsite for Sun. but offsite the rest of the week. what I generally do is check in offsite on fri or sat - rest that day - next day go to the parks. If it is Sunday go to my WDW resort and check in EARLY. then if Disney is also having EMH that morning get on a Disney bus and go. spend that night at Disney (my relatives go back to offsite) and the next afternoon go back to offsite. This works great for me - but others don't like to move for even one night.
the reason I mention this year - last year EMH was on different nights - so next year they could change again.
offsite I will go to each of the Disney parks except MK. It is just to darn hard to get back and forth. However I do park at Epcot and ride the monrail to the MK. then change to the MK one. which is much easier for me. You may not find that a benefit. Everyone is different.
however if you plan to stay offsite - get a good map. Disney does not tell people about their shortcuts. One time coming back from WDW I decided to follow their signs - it amount to 22 miles - but my route was 9 miles.... Now there wasn't a great difference in time - my route had more stop lights. but I hate to waste gas. but Disney is know for this - if there is a short way to go and a long way - Disney will send you on the long way.
you can get a good map for Kissimmee (not Orlando) here
www.floridakiss.com
get use this one
http://www.floridakiss.com/tools/requestinfo/index.php
it is a magazine with several maps of the Kissimmee and parts of Disney. If you stay in the Kissimmee area (where most of the houses are located) - it is a definite help.
for Orlando
www.orlandoinfo.com
Now I don't like their maps - they are very, very small and hard to read - my opinion