Good advice - buy the individual puppy, not gender. Since it doesn't sound like you have reasons for one gender or another (like already owning a particular dog) then being open is your best bet.
If you go to a reputable breeder, they will select your puppy for you (I have never found a reputable breeder in this breed who lets you pick your own puppy - NEVER). The breeder will interview you at length to understand how your family lives, and the temperament of your kids and determine if she has a good fit for you. Whether male or female, this is most important.
Be sure you are well familiar with the health clearances you want in the breed: for Bernese, a breeder should provide BOTH hip and elbow clearances from either OFA or PennHip, CERF certification on eyes, and thyroid clearance from OFA at a MINIMUM. The great ones also provide heart clearances. Don't just look at the parents' clearances, but the parent's siblings to see everything their parents produced - this gives you the best view of the genetic risk. I just met with a woman with a young Berner who's OFAs just came back poor - two bad elbows and one bad hip. She did her homework and looked at the parents' clearances as well as the grandparents, but never looked laterally on the pedigree (siblings). If she had, she would have seen a pattern: while mom and dad both have great health clearances, in looking at all of dad's siblings (5 in total), two of them were seriously dysplastic. This shows you what his parents produce. Given this, you would look closely at any and all litters this dad had prior to the litter you were considering and check out their clearances. This particular dad has 4 litters on the ground prior, and low and behold: at least 2 puppies in every litter he has produced are dysplastic so clearly he is producing this issue pretty consistently. This is what you want to look at to save yourself a world of headache and heartache (and money).
Temperament is very important and very iffy in this breed. Please note that the breed standard calls for an aloof dog to strangers. This is NOT shy, which is a problem. Aloof means confidently and calmly dis-interested. Will allow you to approach, just won't care about you. A shy dog literally shies away from people, things etc. and is stressed about it - that's a problem so be sure to evaluate the temperament of mom and dad - this is your best indicator.
The good news about the Bernese breed is that it is a tight community with good health records. You can accomplish a lot of research and verify clearances more easily in this breed than most by looking at them in the health registry:
www.bernergard e.org and by looking them up at the OFA site at
www.offa.orgBetween these two places, any reputable breeder in the breed is there. The mills and backyard breeders are included only as they are indentified os it is hit or miss with them.
Good luck!