Simply:
Modern day ES stuff is probably Pioneer reference (the STR-DA AVRs, etc). The stuff from the golden days is closer to Pioneer Elite stuff, except I find the ES offerings to be far more enticing but I have not owned any Pioneer stuff myself.
I think it's all a matter of taste, but the old Sony ES stuff is going up in value now and for good reason. If it has ES in the model number, you own something which good build and the performance will be satisfying. There are some absolute peaches in the ES range (my TA-N80ES, CDP-337ESD are my favourites).
My (owned) favourite cassette deck is the TC-KA6ES and it is a superb machine, all metal construction, nice and weighted, audio is superb. People say it is a Nak beater, but it isn't. Some Sony's come close, but the Nak Dragon and other associated offerings are better.
My AVR is an STR-VA555ES which I use as a pre amplifier and to power the rear speakers. For music it is far better (it monsters, actually) the DA2400ES. My friend Stu ignored my recommendation on this and bought the DA2400ES because he wanted the HD audio formats. He eventually saw a VA555ES go on
eBay for a good price, so took the plunge. Within half an hour, the DA2400 was boxed and sold. This is because it will let you turn off the audio processing (needless D/A conversions) on any analogue input and use it as a proper stereo amp. Of course, a dedicated stereo integrated of the same value would beat it, but having AC3 & DTS decoding and 2 5.1 analogue inputs make it one of the most underrated, but best value and superb performing processors I have encountered (and have experience with!)
Best way really is to go to a bake off and compare some models you like the look of. Still tempted to host a Sony ES room at Scalford next year, just not decided.