Lots of 303 discussion going on as of late and I thought it would be interesting to hear peoples thoughts on the best sounding synths and filters when you program them to more or less act like a 303. I know part of the joy of a 303 is you turn it on and it sounds great, no fuss but I also know many of us make a 303 patch first thing after getting a new synth. Definitely some great A4 303 patches out there!
I’ll start off with the Pro2 and the SEM filter, it not being fully resonant immediately gives you a similar feel for how you can tweak it worry free, and the ability to transition the lowpass a little bit towards notch adds some really nice subtleties to it. The envelopes do require you to route an auxiliary envelope to the attack of the first to get the sort of snappy curve you want on the filter envelope (setting the amount to the touch slider lets you play with this live for some nice results) setting the first filter similarly lets you push some more extreme zaps into the second filter also. You have the choice between moog or 303 style glides. Once you get a handle on the sequencer you can get to some great acid type lines going (slew per step takes a minute to get to grips with but is super flexible) and obviously you have a ton of sound design at your fingers if you want to go beyond the traditional scope of acid sounds and make your custom accents with a second sequencer track routed to any parameters you like.
I bet a Oberhiem SEM pro would be excellent… just need to get my hands on one 
