My philosophy on (early game) weapons is as follows. It's pointless to compare two weapons on the forum in a vacuum. Because that's not where a new player is. A new player has a limited set of weapons, mechs, and resources and needs to put together the best package of what they have (or can reasonably buy quickly).
I reiterate the value of early game maximum firepower. Yes it get spread around, but very few large packet damage sources that are common early game (a basic AC20) will reliably one shot an opposing mech. An AC20 to the center torso of a light mech will do it in. But so will more damage spread out. Light mechs are paper. The bigger question is how they do against the more problematic mediums and heavies that can take an AC20 and keep on going. Once we're beyond potential one-shots, the need for a second shot greatly reduces the value of single packet damage sources. So early game new players really shouldn't worry about them.
So instead of asking is one weapon better than another, you should ask how do I combine my available weapons with my available mechs? After reviewing your options, first ask whether or not you think you'll be focusing knockdowns or not. The ability to knockdown opposing mechs in the early game can be VERY powerful. It does 2 primary things. First, it provides called shots for all follow up shots improving the firepower of the whole team. Two, it adds another way to get a reliable pilot injury. This cannot be understated. Getting 3 (or a little later 4) pilot injuries means a pilot incapacitation and three mech parts! Stability damage can be VERY powerful IF you achieve critical mass. It is (mostly) pointless if you don't achieve critical mass and get the knockdowns. So it becomes an all or nothing question for your entire lance. Do we have the tools to reliably get knockdowns? If so, design the whole lance around it. If not, focus on total damage and ignore stability damage as it will rarely come into play.
As an example, do I use a PPC or a large laser. The PPC has a lovely 20 stab damage. Which is utterly pointless if your entire lance does very little stability damage. So go with the large laser instead. However, if your other lance members are a LRM boat, a SRM boat, and a mech with significant stab damage from AC/UAC/LBX, then suddenly the PPC's stab damage becomes much more relevant and may be the difference between a knockdown or not.
So once I've decided, knockdown focus or not, that starts to guide our direction (and you may need to come back to that question if after building out your lance you realize you should have gone the other direction). The next question is what is my baseline damage for the mech in question? The best way to do so is to assign MLs to every possible laser slot and then add heat sinks to come out heat neutral (or close to). This gives you a base measure of damage for that mech. For example, take an enforcer, add 5 medium lasers and heat sinks and you come out with a base 125 damage per turn. Then modify from there. You may decide that is great and not do much. Or you can start to tweak it. Perhaps replace a medium with a large. Okay it adds 15 damage but takes 4 extra tons and 6 extra heat. Is that worth it? Well, enforcers don't go very fast so it might be if you have consistent trouble getting it into ML range. Or perhaps you max jump jets and it generally stays with the group in which case the 5 MLs might be superior. But the point is your 5 MLs gives you a base. The enforcer comes with an AC10, why not keep it? Well, it is an awful lot of weight for 60 damage? But perhaps you're running knockdown so the AC10 is better even though it's overall damage is less. Just be aware that the same mech could be putting out more total damage with lasers. Which mech goes with your plan?
In assessing weapons remember the speed and role for the desired mech. A missile centurion may be outpaced by the rest of your lance and so the small laser you put on NEVER comes into play. Until that one attack and defend mission where you run out of missiles and need to wade into melee combat. Another example is the idiocy of the small laser on the urban mech. Sure, the mech was designed for short range, but most missions that small laser will never get used. Better to turn it into the third jump jet or more armor. So when calculating your damage, remember to only count damage that is likely to happen enough times to be worth it. ie. don't add the small laser damage to your urban mech total damage calculation. It will rarely happen, even in cities. This is in contrast to Vulcan or Pheonix small lasers which will regularly get used.
So make a potential lance and see how the damage adds up in total and does the group make sense? Do you have the roles you want and the mech to fill it. Are all your mechs trying to do the same thing? Is that a good thing or a weakness. Do your close range mechs have the mobility and survivability to get to their targets? Do you missile boats have sufficient ammo and what do you do when you're out?
As far as heat balancing goes my general rule is as follows:
Build so it can alpha 3-5 times before overheating in a heat neutral environment.
If the mech commonly jumps, build weapons to have your alpha equal your cooling.
TLDR:
Fill your mech with medium lasers first and balance your heat. Use that as something to compare your out of the box crazy build against to see if you would just be better off with medium lasers.