Since starting my post-doc, the lab I am in has had a couple of other post-doc candidates come visit. Soon it will be time for the 1st year grad students in the department to pick which lab they will work away in for the next four to six years. Whenever either happens inevitably the discussion of how to choose a lab comes up. It is not a choice to be made lightly. I have seen friends in grad school who choose the wrong lab and were tormented for years. Their PIs being masters at undermining confidence leading to the students feeling trapped. At the same time, I have seen people who realize the lab is not the right fit (usually the PI is a perfectly fine person, just not the best mentor for said student) and switch to another lab without a problem. Ideally you want to avoid the latter and most definitely the former is to be avoided if you can.
I know people who say you should join the most prestigious lab you can. The idea being you will have great connections and a good shot at papers in high impact journals. I personally think this is a bad way to choose a lab. To me the most important criteria is whether this is a lab you can see yourself working in for the next 4-6 years. Does it fit your learning style? Personality? If a PI is a micro-manager and you prefer some space, it probably is not going to be a good fit. If you need someone pushing you then a PI who is more hands-off is not the mentor for you. If you are open to possibilities outside of becoming a faculty member at a research university in the future, would the PI be supportive? If the answer is no, you should look for another lab. Does the PI care if you work 50 hours/week instead of 80 hours?
I am a big fan of talking with people who are in the lab, who have been in the lab, and those who choose not to join the lab. Find out why the made that choice and whether they would do it again. A warning sign if you are visiting as a post-doc is if the PI only lets you talk with certain people in the lab and not others. Typically this indicates they are hiding the malcontents. Ask yourself if the people in the lab are people who you wouldn't mind being around for the next few years. First years have a slight leg up on post-docs since grad students typically rotate in labs before picking one, giving them time to truly get a sense of the lab & the personalities in it. Lab feel is subjective. You have to know yourself which takes a certain level of maturity and confidence. You have to remind yourself it is your education, your training, your future especially when others are doubting your choice. Other factors should come in mind but they should be used to decide which of the good labs for you that you should join.
Factors in choosing a lab (in order of importance in my mind):
1) Fit - A) Will the PI be a good mentor for you? B) Is the lab environment conducive to you learning, working and keeping your sanity?
2) Science- does the work interest you? excite you? You are going to be working on these projects. If it doesn't excite you then you probably won't want to be there for long.
3) Funding- What is the grant situation looking like? A great lab fit-wise that is hoping to tackle exciting topics but without money it isn't going to happen. Not to mention it can be demoralizing.
4) Prestige- Connections do not hurt and high impact articles do help down the line but they are not everything.
Any I am missing? Let me know.
I typically (not all) find the PIs who sell prestige as being the most important are usually the one's to be watchful of before joining. They try to sucker students/post-docs in with talk of Science & Nature papers. Be skeptical if that is their biggest selling point. Remember if they want you to join their lab it means they think you could do high quality work, that they see your talent and that you are valuable. Guess what? If you join a different lab that is a better fit personality-wise, most likely you will do high quality work there as well but will be a happier person. Life is too short to waste it on taskmasters who want to use your abilities to keep their own prestige high.
Now picking a lab is not perfect. Remember plenty of successful scientists have changed labs and done well. If a lab is not working for you, you can switch. It will work. It won't set you back.
Programs need to remind Post-docs and grad students of this fact. Obviously the poor mentors are not going to.
Updated as per the suggestions of Katie at Minor Revisions:
There are a couple other things to keep in mind when joining a lab.
A) Lab space- Does the lab have physical space for you? Will you have your own desk? Bench space? What are the common areas like in the lab? Now part of this falls under funding but there are times when labs expand quicker than lab space is given. When I first joined my grad school lab, I had to share a desk and lab bench space. It sucked but I knew it was a two month situation until a visiting scientist and a couple post-docs moved on. For other labs this can be a common problem and people are placed in random spaces in the building, sometimes isolated from the rest of the lab. Some like this, other sdo not. Once again it is subjective based on what you can tolerate and what works best for you.
B) Politics- This ties into the lab environment and the science. Your work is not done in isolation. Your lab will be in a building with others and be part of a department/program/etc. You may collaborate with others. There are other people in the field. It can be tricky. Is there support for you beyond your lab? Support to teach you how to navigate turf wars? In a collaboration is everything clear on who is working on what? How authorship will be taken care of? Are there common resources you can utilize to make your life easier in the department (or will they make your life harder)?
C) Is the lab organized? Are there lab responsibilities that are evenly assigned? Do they have regularly scheduled research meetings/journal clubs? Are they productive meetings?
The key is asking lots of questions before joining a lab. Find out as much as you can to make an informed decision. Find out what is beneath the glitter to see if it would be actually gold for you.