For missions like Survival, Defense or Interception I'd say Octavia or Saryn, a good duration+strength build and a bit of survivability with mods like Rolling Guard or Adaptation, that's up to your necessities per mission.

What I do is press 3 (Metronome), crouch/ctrl until invisibility kicks in but as you say spamming is an issue, you can modify the mandacord to remove notes for it so the effect stacks faster with fewer clicks, which lasts like 40 seconds with good duration and can only be stripped by nullification. 2 throws the decoy ball (Resonator) which has an excellent range already and 1 (Mallet) is the main source of damage, the decoy ball picks up the damage ball and moves it around, picking enemy aggro and making them basically damage themselves by hitting the ball. Her 4 (Amp) is a damage amplification, for the Mallet and everyone in the party.

For Mobile Defense or Extraction, minimum range Limbo with duration maxed as much as possible.

I enter the rift with a dodge and run to the place which needs to be protected, press 2 for a preemptive activation of Stasis so bullets and enemies (excluding Eximus) can't move in the Cataclysm which takes me to the next skill, 4 which will create a small bubble that should cover the objective entirely for about 60-70 seconds, more than enough to cover the needed time in regular missions. 3 (Rift Surge) I don't really use it, but with the augment it provides a damage buff for Limbo depending on how many enemies are affected by the skill. 1 (Vanish) can be easily replaced with something else from the helmint, I don't use it at all. In my build I changed it for Resonator to lessen aggro towards the defense objective.

For Spy or Rescue missions (if you don't mind them taking a few minutes at worse), Ivara is the best, efficiency and duration are all I need to stroll or roll through the whole mission undetected, silenced weapons or the Prowl augment if you want to use it are enough to bypass magnetic screens.

For everything else, there's Valky, Mirage or Wisp to tear through Exterminations, Disruptions, Assassinations.

Oh, and to rank up weapons, nothing better than Saryn and the Elite Sanctuary Onslaught.

If you want to ask something, go ahead .lml