This is a very subjective issue because we all hear and like different things, and play different guitars and amps. Giving advice is therefore very difficult, but I hope the following helps you on the road to finding your personal tone Nirvana!
1. Because choosing the right replacement speaker is such a daunting task and an expensive exercise, having come across this excellent you-tube video I thought it was worthy of inclusion here. The clips are particularly helpful because exactly the same amp and speaker cabinet are being used in each instance giving a truly meaningful and fair comparison.
I think this is an excellent comparison tool to help get folk on the right path:
2. In addition, manufacturers often have their own sound clips on their websites. Here are some: