I've been on several lab visits for PhD's and was wondering: how much weight do I give to my gut reaction and first impressions?

i would give priority to them. i didnt and have regrets.

I relied on first impressions. When I came to visit the lab, they were all nice and say it's a good lab and so on, but now I am here, I just realised that they would never tell a student coming to visit their lab that it is not really good working there, because they must feel morally faithful to the lab. When I came here, I found out the truth...no supervising, left alone without a direction... Good luck and make a wise decision, but don't expect it to be really funny experience.

I usually give a lot of respect to my gut reactions (as in the past I hae been correct on many occations). I would tend to think that if you have a bad feeling it is usally based on something. I went to a PhD interview in a lab where I had a really bad feeling - I turned down the offer of a PhD there.... I have since found out that 2 students in that lab have put a formal complaint against their supervisour.... I had a lucky escape!

Of course it is unlikely that people will tell you their lab is rubbish and you should run like the wind, but by asking them you will be able to form some impression from their reaction. If all other things are equal then your first impressions are probably worth following. Three years is a long time to spend in a miserable environment.

Think about everything carefully - first impressions are great but I personally wish i had looked at other things not connected to the project more objectively such as where it is - social life , distance from partner/family. I didnt consider this as I was so bowled over at getting PhD I wanted and now find I have a very isolated and unhappy life outside of work - living in a very small village hundreds of miles from anyone I know and woking essentially alone. Try to picture a typical week living and working there...