Sequential Circuits Prophet 10 by rpmedia
This really nails the classic Prophet sound, full and weighty, with the great additions of velocity and aftertouch for enhanced performance. Plucks, pads, e-pianos, brass, all sound great on the standard 2 VCO + VCF per voice design, shaped with separate ADSR envelopes for filter cutoff and VCA amplitude. The Rev 4 may seem quite limited compared with modern designs, but the sound is incredible and it can still surprise with sophisticated timbres, especially when deploying the poly-mod controls.
It looks and feels like a classic Prophet and the 10 voices give a lot of depth to the sound and a significant reduction in voice stealing compared with the 5. It sounds incredible without any effects at all, while a touch of reverb only serves to enhance it further. Velocity and aftertouch allow you to take it further than the original Prophet 5/10 make it wonderful to play.
The large control surface and simple layout make it a joy to program and while some design elements may seem a little odd for users of modern synths (stepped filter cutoff, voice allocation method, patch selection), they don't cause problems for me and in some cases can be changed - e.g. voice allocation can be switched to round robin if you prefer.
With OS 1.5.2, it adds poly-unison, giving two voices per note with 5 note polyphony, for extra thick sounds when desired - 4 oscillators per note! This is also very useful when using Osc B for modulation as an LFO rather than as a sound source, allowing five voice polyphony while retaining 2 oscillators per note.
The "vintage" knob is perhaps a little gimmicky, but can be quite effective to add some additional variation in sounds, although I generally only find it useful on settings between 3 and 4.
It may seem pricey, and indeed it is, but worth it for the experience IMHO, a wonderful synth.