Again, your current supervisor is a goldmine of information on what labs are the most productive and that you'll be happiest in. However, bear in mind that the character of labs change with the people that inhabit them, so things might be different now than what your supervisor may think. By keeping up with the literature, you can get a feel for which people and labs are producing cutting-edge science and which might have cooled down a bit. It's also perfectly fine to e-mail authors of interesting papers directly about working with them. You can learn a lot about a person by surfing their uni's web site and reading about their work and projects there.
Funding is very important when choosing a research environment.
This is especially so for molecular-type projects that may require that the funding be entirely in place before you even start. In labs with lots of grant money, funds can often be shunted around to help you get your project started. You can then apply for your own funds later based on the pilot study. Several more subtle issues may also come into your decision of choosing a research environment. A younger supervisor might be more on top of current trends, but may also be busier and less likely to put you on to the choicest research projects.