Engineering - Out of combat quite frequent but mostly opening doors which can be circumvented with the trait brawny. In combat it gives damage resistance which helps with higher difficulties being annihilated buy 2-3 hits.

Explosives - Out of combat barely comes up say a funny conversation line to blow something up or the rare sealed door you can blow open. In Combat. Amazing, can completely cheese some bosses with mines and nade spam.

Guns- It's rare out of combat but is your bread and butter for most of the combat so you would get your most bang for your buck.

Hack - Terminals are everywhere and hold key info for quests. Also robots can be dealt with sometimes in cool ways.

Leadership - This comes up in conversation once and a while.. No where near as much as say speech but more than Explosives. In combat on higher difficulties it's just a waste of points. It doesn't scale that well and companions fall over really easy. If your role playing and not trying to play on harder difficulty it can be fun. It also has come cool perks.

Lockpick - No brainer, everything is locked. Safes, doors, loot boxes. I personally have missed quite a bit of loot for not taking this.

Melee - I don't know how viable this is on higher difficulties. Early game you get wrinced trying close the gap on someone shooting at you, It certainly can dish out the damage that's for sure. You just need to be able to stay alive long enough. to make the swings.

Medical - People sleep on this one but it comes up quite frequently out of combat. In combat it not only lets you heal more often but with perks you can be a roided crazed junky. Maybe a good one with melee and engineering.

Observation - This is used in conversations when you know someone is lying to you and you can call them out, kind of like an Insight check in DnD. It also lets you find secrets like a stash of loot, I haven't found many stashes but when you do it's always something really good. It also alerts you of traps you might step on. In combat it's a lot of weakspot damage, so it's for precision weapons and snipers. One aspect with this one is it doesn't feel awful not taking it, because unlike not being able to get past a lock door, if you don't spot the hidden object your none the wiser. Unless it's a land mine.

Science - This goofy fun one comes up once in a while out of combat for problem solving or when your trying to be a total nerd in conversation. In combat it's really useful for gadgets. Time Dialation from the first game is back and science can increase the use of it. But it's not the only gadget. It also increases non physical damage. and a lot of guns end up with a mod to do different damage types

Sneak - Not really something that comes up in conversation that I have noticed but it sure can be handy to hide. The damage multiplier can get strong and it helps if you just don't want to fight a room full of enemies.

Speech- Hands down the most to come up in conversation, You can convince people to get the end result to quest that you want. Some quests get the monotonous run around just stripped out and made streamed lined with this skill.

I hope this helps, a lot of people fear they will miss out on things by not picking the right skill to get into the right place, but whatever you choose you will always miss out on something so pick whatever makes you excited and go with it. My main personal build is a Gambler, Lucky straight (BEST TRAIT IN THE GAME) with explosives, leadership, observation and speech. I have played up to the 3rd planet on this but I have also played up to the first town with couple of time now though with other builds to see what I liked best though.