Prob the 480L (although the Relab one was first and equally good) since you get so many algorithms that sound great with synths and percussion, highlights being halls and rooms.
RMX16 if you like the ambience program sounds.
There are EMT style plate alternatives from Soundtoys, Waves, Valhalla, but the BX20 you will not find anywhere else. The Pure Plate is a stripped down version of EMT 140.
The Eventide H910 is one of the best and vibiest delay plugins, but also available native.
For eqs and what not
The newer versions of SSL strip and Bus are ridiculously good emulations (I know the hardware well), but use a lot of DSP. I found these much more accurate at capturing the dry SSL sound than the Brainworx versions and more dimensional than SSL Duende, which is rather old at this point. The Cytomic is also good, but has a little less character than the UAD.
The newer 88rs is more neutral in sound but similar quality.
The Softube for UAD Chandler Curve Bender is a great bus eq, with color and more forward than Massive Passive, which is better for acoustic/more relaxed work
Also like API 550 series for channels, eg 560b for kicks and 550a for guitars.
1176 collection (the newer one, I consider the black 1176LN to be the most like real thing) and Distressor.
The gray LA2A is the best
The 1073 is much better than the Slate one, which is too pointy in mids and the phase interaction is wrong. I do not consider it a must have for electronic music however.
For surgical eq try TDR Labs, cheap and high quality.
Personally I use DMG Equilibrium, also very popular with mastering engineers.
If it were me for electronic, for most mileage I’d get the SSL console bundle and the 480L
Then get the new Valhalla delay
Then BX20 or AMS
