Everyone has their own favourites in Chinatown and I'm yet to meet a group of people who all have the same favourite.
I'd avoid Plum Valley though as it's so blimmin' expensive and the food's not all that wonderful.
What type of experience do you want? Also what meal will it be- luncheon or dinner as then you've got dim sum type places to throw into the mix.
The last two I went to were for dinner and was Golden Dragon- huge restaurant, pretty generic, have been going there on and off for many years, you'll get to have whatever you like there and the dim sum's not too bad. I wouldn't say it's special but in terms of chinese it's alright.
The previous was dumpling's legend- their xiao long bao (dumplings with soup in them) are very nice and their food's pretty good and again quite generic chinese food.
You'll get generic chinese food in most places on Gerrard St (I've been to an awful lot of them) and pretty bog standard atmosphere. When I go back, which will be this weekend I'll probably head to dumpling's legend with my mate. If I'm in a group I'll go to Golden Dragon.
I've heard out in Queensway is where some other good places are as well.