NeuroVoider

What I did was pick Fortress with the Self Repair skill. Play through the levels like normal, not venturing too far off the path. Only kill what lies between you and the objective. Once you have the option to teleport, do so. Pick up whatever is in your way. After each level, quickly equip what you want to put on your Fortress, then proceed to the next level.

I didn't take too much time looking at the stats of my equipment. Simply, if it had a higher rarity, I equipped it. Once I had all orange, I fully upgraded it, until I found another Orange item. Then I would equip that and fully upgrade it. For weapons, I stuck strictly to rocket launchers only. I stuck with very high damage so I could easily take out the boss fights quickly.

Play the special levels as they will reward you with a level skip. Whatever level you skip, the next one will be easy so don't use a level skip on the level before the boss, as it doesn't affect the boss fight. Instead, use it on the level right after the boss fight. If you're coming up to the final boss and you have a level skip, use it.