We get calls on this topic frequently and the answer is pretty straight forward, go with what you feel the most confident swinging.  No one knows your swing better than you.  Odds are, most of you have played or have been playing for some time and have had a chance to test out various equipment over the years.  If you haven't, that's fine, we can give you some suggestions below on how to get this dialed in.  

Slowpitch

1) Length -- this one is real easy.  All mens slowpitch bats are 34 inches.  So we all get to work with that.  

2) Weight -- the general rule of thumb is you want to be swinging the heaviest bat you can, the FASTEST.  I have an entire blog on this topic and will provide a link below to that blog.  Give this a good read and you will know what I am talking about by the end.  

link to blog --  https://homerunderbybatsonly.com/blog/

2) Balanced or end load?  The answer is it all depends on the hitter.  The blog link above also gets into this somewhat, but will expand below.  All things equal, an end loaded bat will out distance a balanced bat due to the stored mass at the end driving through the ball.  The downside to end loaded bats are they are harder to swing consistently (especially super end loaded bats).  I dont know about you, but I rather hit .800 on the weekend spraying the ball all over the place, than batting .400 and hitting 2 balls 450 ft with the rest being largely trash hits.  Truth be told from my experience doing hitting instructions as well as playing ball are most people choose an end loaded bat because of potential distance, but shouldn't be swinging one.  Knowing your swing, having solid fundamentals and being able to repeat this time and time again is the key to being a legit hitter.  I am not saying you shouldn't hit an end loaded bat, what I am saying is just because you see 50 people swinging a certain bat in your league doesn't really mean you should be.  My suggestion is to try out some of your buddies bats and start there til you have enough reps under your belt to get a feel for what you call consistent.  I personally over the years have migrated from a 28 heavy end load to a 26.5 slight end load or 27/28 balanced and can hit the ball just as far.  That is what works for me, now.  

3) Barrel size -- this is very important.  12-12.5 inch barrels, aka short barrel bats, generate more bat head whip, are generally easier to swing, but also have a smaller sweet spot.  13-14 inch barrels, aka long barrel bats, are generally more forgiving as the surface area is larger, but depending on the balancing, can lag or drag and harder to swing.  The only way to figure this one out is to try them out.  

4) Handle Flex -- seeing as now most slowpitch bats are 2 piece, this means manufacturers have the ability to adjust the stiffness of the bat.  This has only been in play the last year or so meaning when the 2 piece bat first came out, it was simply a wobbly, flimsy feeling bat.  Typically speaking people with faster swing speeds tend to favor stiffer bats while players with slower swing speeds favor bats that flex more.  There is no real benefit to either performance wise, its more a matter of feel and what you prefer in my opinion.

5) Grip -- Most people don't consider this, but bat grip / style can make a world of difference.  Do you like the knob built up, rope style, stock grip, hockey tape, thin or thick, spray or no spray, etc.  Knowing the detail is important on choosing a set up right for you  

6) Manufacture -- this is very important as not all bats are the same.  As bad I want to bash some manufactures, I am not going to do it nor am I going to boast on the ones I like.  Everyone is different and every bat swings that much different as well which is why there are 1,000s of bats to choose from.  My suggestion is to go to a demo day if they come to your area or again, grab some of your buddies bats and try them out.

In summary, there is not any magic formula anyone can give you to say hey, this is what you should be swinging.  Experience pays and there isn't any substitute for it.  If you are largely in the dark and never played ball in your life, my suggestion would to be start with a 27 balanced bat and tweak it from there.  

Baseball

Length -- I do not believe in height and weight charts.  Using those charts it says my son should be swinging a 28-29 inch bat which is ridiculously large in his hands.  I have him in a 27 as it looks right.  The way I size kids is to have them stand up straight wearing their cleats, hands down to the side relaxed.  The knob of the bat should come slightly below the wrist line from the floor where the hand connects to the arm.  If the knob is above the wrist, its to long, if it is near the bottom of your hand near the finger joints, it is way to small.  A longer bat will give you more leverage, however, if you cant control it nor handle the additional weight, its a waste.  For taller players, anyone over 5'10 needs to be in a 33 inch bat at minimum in my opinion.  If you think a 34 can be swung consistently, my suggestion would be to go with one of those.  34s are not for everyone and I for one know from experience (I am 6'4).  I personally swung 33s in college.     

Weight -- Once you figure out the size, some may be able to select the drop.  Most dont know this, but all baseball bats weigh around 1-2oz OVER sticker.  Meaning if you see a -10 sticker, actual scale weight could be >= -9 or so and so on.  This can be very misleading and honestly have no idea why bats cant be designed to weigh what they are suppose to.  Depending on the make and model, this weight spread can vary greatly.  Have your son try out a few bats and see what he prefers is my suggestion.  Again, heavier the better if he can generate similar bat speed

Balancing -- swing a balanced bat.  Same reasons I outlined above.  Easier to swing and control and seeing as ball velocity comes into play for baseball, you dont need anything making things more difficult.  Launch angle, hand position and bat speed are crucial.