The more searches, the better, but that's only one factor and it's only the "potential" searches. Also, if your are using "broad search" then you need to know the number is inflated. Look at "phrase search" and most importantly, "exact search". If your exact search numbers are high, then that may be a good one.
But if you are only using the google keyword tool, you are missing out on other information you should be looking at, depending on what you are doing with the domains. For parking, you want that number to be as high as possible, but you also need to know what the keyword bids are running.
https://adwords.google.com/select/TrafficEstimatorSandbox can help with that and it will also give you a more general idea of traffic. There too you can use broad, phrase, and exact match to see what each one offers.
If you are buying to resell, then search numbers are interesting, but may not mean much to your buyer.