The "Tea Party" is currently at Pizza Planet in the park, so I assume you mean a charcter lunch or dinner?
I like to take my time and let the kids have a nice relaxing time when doing a character meal, so Id always opt for dinner rather than lunch and losing valuable ride time!
The characters alternate, so could be any! Tigger always seems to be there though. The characters are there 7pm - 10pm. They come out for a bit, sit with the kids, sign autograph books and pose for photos. Then they go off and swap with other characters.
It's good fun, and the kids will love it. If you booked Half Board plus you could use your vouchers for charcter dining at Lucky Nugget Saloon so that will probaby save you a fair bit especially with the current crap exchange rate on the Euro.
Cafe Mickey is a but nicer in my opinion, but you can't use Half Board Plus vouchers for there, only Half board premium which obviously cost more.
Id definitely make a reservation, especially if you are travelling in busy periods. Just make your booking then call the dining reservations line* give your name and date you would like your meal and they will give you a 20 min time slot to arrive. That way you dont have to queue and wait for a table or have to find an alternative if it's full on the day you want.
*The dining reservations number (once you've booked the actual meal) is:
0033 160 30 40 50
Hope this helps,
Lisa.