i think coilovers would be simpler, simply because with the front struts once you compress the OEM springs you would have to compress your lowered ones to go on the OEM strut, whereas coilovers are a complete unit.
The opposite is in fact true, "lowered" springs will be shorter and therefore probably/possibly not need spring compressors in order to mount to the shock.
Generally coilovers will still need assembling, although with the adjustment you can probably assemble without compressing the springs.
Not many of the coilovers, certainly not at the cheap end, are proper 2 1/4" parallel spring type, they may be for the first few inches of spring but will end up as a normal pigtail fat one. Generally this is hidden in the front wing so nobody knows
I'm not sure if any of the manufacturers have proper coilovers for the rear, everybody shows pictures of them in the adverts but irl I believe they all have the spring in the OE position off the shock. (would love to be corrected on this if anybody has a proper rear coilover).