Changed our Minds - Are we being Mean

The vicar of the original church may be disappointed, but I am sure he will understand and want you to be married in the church that you feel most comfortable in.

Have you met the vicar from the new church though? If you haven't, I would suggest doing so before you make any firm decision. It seems that it was the personality of the first vicar that really made you decide on using that church, so you don't want to swap to the new one before meeting that vicar, just in case you don't get on with him when you do meet him! The venue may be more important to you than the person officiating, but for me, it would be more important to get married by someone I felt comfortable with in a building I didn't like as much than the other way round!

It is your day so your choice. I agree with RGS, make sure you are truly happy with the other church and I wouldnt say anything to the first one untill you have booked in the new one. It is hard when you have met someone and then have to say no, but it is your day, and you need to be comfortable. Keep it simple, you don't have to say you have found another church, send it in email, and just explain that having looked at your options you now want to go another route for your ceremony so won't be proceeding with booking, and thank them for their time. that is all that is needed,

Not a church, but I had similar feelings when we went to look at our venues. One was really lovely but unfortunately didn't have accommodation on site, which was really important to us. Also some access issues - nothing insurmountable, but when we went to the second venue (which we eventually picked) there were none of those issues.
I felt bad, but just sent a quick email to the first venue saying 'thank you, but we've decided to go with another venue on this occasion', and thanking the staff (who were really lovely).