Old analogs are a pain in the arse... they have no MIDI, no presets and most have no memory and their oscilators will drift and detune with temperature changes so you'll have to be on your toes, also, if you want to buy a Moog System 55, which is the most desireble vintage modular synthesiser, you will have to dish out a big amount of money, 30.000 Euro's for one thats working and you'll probably have to spend that amount of money again to get it in top notch shape.
Most of the analogs are also monophonic although there are later era analogs that are polyphonic, the king of those is the Korg PS 3300.
Modulars are not easy to work with, switch on a Moog Modular, press a key and you'll get not the slightest beep, you will first have to patch several modules together with patch cables before you even get a beep.
However, nothing comes close to the sounds of those things, a well maintained analog will trash any digital into the ground, sound wise they rule, analog modulars have no limit in what way you can use them, the ways you can patch them is limitless, they can produce sounds no digital can ever dream of producing.
In essence you are creating an unique synthesiser with every patch you make, tailored for the sound you want to have.
Another thing is, and now I'm getting mean, anyone without any talents can buy a digital synth, find a preset and make a noise, you've got everything at hand, if not, go online and you'll find a patch for a sound you want, result is that eveything will sound alike, in the late 80's the Yamaha DX7 came out and it was WAY more affordable than anything else, everyone and their grandma used the bloody thing so every house song from that era sounds about the same because in 99.99% of the time they were using that synth.
Luckily since the late 90's people have become bored with digitals and there are a few companies who are building analogs again, now build with far stable components so they'll be less a hassle to tune and keep in tune, also they've got patch memories and so on so you've got the best of both worlds.
^^ Thats a link to a demo of an Eminent 310U which isn't entirely a synthesiser but an electric organ it was also the first commercially available string synthesiser, feed it through an Electro Harmonix Small Stone Phaser and you get that sound, Jean Michel Jarre used the Eminent throughout all his albums.
Thats how inventive you had to be in the old days, there were no samplers, you had Mellotrons in those days, that was a device with a looped tape connected to each key which played the sound you recorded.
OMD used it for the lead sound on Maid Of Orleans, the base sound was a violin.
Enough old guy rambling.