Argon-seeded H-modes in low triangularity pumped-limiter-like, and medium to high triangularity divertor, configurations on JET are described, focusing upon ELM effects. Appropriate fuelling and seeding strategies in each geometry have combined good confinement with density around the Greenwald level, accompanied by ELMs shown to have explicitly Type I character. For lower triangularity, argon injection leads to a reduction in normalized ELM energy losses averaged over several fluctuations, relative to unseeded scaling at comparable frequency and confinement but lower density. This generalizes a similar result in earlier studies. Optimized seeding tends always to decrease ELM frequencies too, so that average energy efflux in ELMs is significantly diminished, down to only 10% of input power in the lowest example included. At least for lower triangularity again, electron pedestal temperature is cooled by argon, tending also to lower peak pedestal pressure before each consequently smaller fluctuation. However, pedestal density is raised, and at higher radiation fractions this can restore unseeded peak pedestal pressure and roughly ELM size, but still at lower frequency. Underlying physics of Type I instabilities defined by pedestal collisionality appears to prevail in all cases both without and with seeding. High performance H-modes with both reduced core transport plus moderated steady and transient power loads through added impurities therefore seem to come closer to a fully integrated scenario for Q = 10 operation in ITER.