Just use rhino and you'll never have to worry about dying. #rhinoislife

For the most part, you have the correct idea about what faction is weak to what. I was told not to long ago that a good all-round damage is blast+corrosive or corrosive+cold since the effects are favorable for most things when they proc and the aura mod corrosive projection is a safe bet to use for most frame set ups, especially ones that have few offensive powers or must rely on their weapons a lit (ie. Trinity, Nova, Limbo, Loki to an extent). I've never known someone to make different builds for each faction, but if you do that, more power to you. Here are the two things I take with me not matter the faction. I'm going to sound like a salesperson for a minute or two here: If you're willing to put 3 weapons (yes, 3 built weapons) and the effort/ resources it takes to build or buy them then the Lesion, aka the mutalist Tipedo, is a pretty good melee weapon. I never find the need to switch it out and it's actually quite useful for a lot.of different situations including sortie level stuff and long (2000 cryotic, over 20 rounds/minutes) runs. Several things make it great. It has a nice base attack speed with decent base damage. It does slash which is also nice. It does something a bit different than a lot of other weapons. Everytime it gets a crit for any reason, it gets a temporary boost in attack speed and it then does toxic damage. This opens up the possibilities for crit builds status builds which can work to a lot of success. But the problem is it only had a base crit chance of 10%. Despite that, it's a really nice all-round melee weapon. My favorite weapon is the Sonicore and it's an arm mounted pistol. Be aware of it's hefty cost to build, it takes a decent amount of oxium. But I find the price is worth the shear utility. It does innate impact damage, has an area of effect/blast radius and best of all it knocks enemies over on their asses so they must take some time to get back up in order to begin attacking you again. What this weapon lacks in base damage it makes up for in this unique ability to knock things over and send enemies flying. You can make an entire building for this (like I do) and mod your Sonicore so that it has max impact and blast damage and adding a little fire rate doesn't hurt either. This way you can send enemies flying across the map and [u]even eject enemies off the map entirely.[/u] Unfortunately, when you get to higher levels the damage fall of is quite noticeable. But the the cc mentioned before doesn't change, so you can still defend yourself and send enemies into orbit if you so need to. It's a great weapon for squishier frames

Corrosive is good against armor I don't think it is usefull enough to mod it for killing infested. Radiation works well against robotic enemies, so a Corpus map with lots of those might favor radiation instead of magnetic. But unless you do really high content damage/crit trumphs all. Also a statusbuild with viral will work wonders.

Tigris prime 100% status build, primed point blank,hells chamber, sweeping serration, punch through mod. Akstilleto prime (or euphona) the usual primed pistol gambit and target cracker, barrel diffusion, lethal torrent, your damage mods. (Primed pistol mutation for akstilleto) The melee weapon I use galatine prime or nikana prime. Ohma is amazing aswell. Edit 1: corrosive for grinner actually unless you can remove all armor then it's radiation/viral.

Just use boltor prime and you'll be good(unless they nerfed it)

Try plasma sword with spoiled strike

Gun. Armour. And you're pretty set to go!

Use Hek and get it's SM mod and use a maxed Hells Chamber and a base damage mod. Then try to get the status up to 100% with the damage+stauts chance mods. The least amount of mage I am doing is 800 impact.

I hardly ever run specific setups for factions... If the weapon is crit based, then I boost the crit as well as whatever raw damage type is its strongest, then put on corrosive, gas, blast, viral or any combination of them. I almost always use corrosive on my melees regardless of faction (which btw, corrosive is better for grineer than it is infested and viral is better for corpus than it is grineer) but sometimes use a viral config or gas if I'm using Naramon and / or a stealth frame. Ideally, I always have multiple combos on one config whenever possible (corrosive + blast + gas being my favorite). Also, look up the channel Distant Observer. The guy has some crazy builds and combos.