This depends on what you think is more important. Do you want faster, more efficient damage or do you want to have much more success against FG's that require you to use lobotomy? What I did was upgrade my Pillars/Pendulums first after RoLs, then Electrocutors, then Fractals, then Archangels, then Hopes.
Basically, two choices:
1. Upgrade 2 more Lobotomizers - Helps for pretty much all FG's, most notably Osiris (his Pharaohs and SoFo will eat you alive, literally), Fire Queen (completely shuts her down), Destiny (renders Fate Eggs useless), Morte and Incarnate (so Retrovirii don't destroy your RoLs), Lionheart (don't allow his Crusaders and flown Eternities to Reverse Time you to death), Paradox (stops his RoL's from making quanta to Miracle/Bless his creatures, stops Deja Vu's from multiplying), Elidnis (stops his main strategy of building up Forest Spirits, stops Ulitharids from making your RoLs useless), Akebono and Gemini (stops their Momentum creatures), Dream Catcher (rid his various creatures of skills), and Dark Matter (stops his Nymphs and Otyughs from doing what they do).
2. Upgrade two Archangels, replacing two Golden Dragons - more efficiency in getting your high-damage dealers out fast. A little worse at sudden blasts for those Miracle FG's, but still the much preferred choice.
Don't let the huge disparity in length between the two choices fool you. Either is a good option, it just depends on what you want to do, and what you're seeing often.