I have spent countless hours finding what I believe to be THE top of the line synths for VST for use with Live in terms of flexibility and sound. Whilst they are not the cheapest you certainly get what you pay for. To me this list is unbeatable in the VST realm:
* Lennar Digital's - "Sylenth1" synth (
http://www.lennardigital.com/modules/sylenth1/ ) imo wipes the floor with the previous suggestions for trance - it really has to be heard to be believe and most professional reviewers have likened its sound the the HUGE Access Virus hardware synth. It probably has the best sound of all but it imo has the least flexible routing, however the developer is currently working on addressing this.
* Native Instruments "Massive" synth (
http://www.native-instruments.com/ ), initially I did not like this synth, but after forcing myself to play with it for a LONG time, I came to realize that if you ignore the included presets and dig deep with programming it ( and you can go pretty deep with its modulation routing ), you can get sounds that are incredible fat and full and very versatile - the one trademark of it's sound would be the word "dark" - I don't think it is extremely suited to high pitched material but for pads and basslines it is awesome,
* GForce's "impOSCar", "Oddity" and "Minimonsta" synths (
http://gforcesoftware.com ), are by far the most versatile trio of the lot, and comprise of the guts of my synth arsenal and are easy and enjoyable to make your own sounds for, I could not live without them now, and for basslines Oddity is simply fantastic and easy to use,
* and Way Out Ware's "TimewARP2600" (
http://www.wayoutware.com/ ) ( Amazing for trance sounds, and in general has a more analogue sound than most synths - it's like it is always a little "out of control" to speak.... ).
From my own experience I thought from the moment I heard it that reFX Vanguard had a "cheap" sound with a "narrow" - very pushed mid freq - frequency response to my ears - I don't like the sound of it's filters, I think they have a somewhat plastic quality to them. If you open up the filters on Sylenth1, impOSCar or TimewARP2600 there is no comparison - to me they are warmer, smoother, brighter and more responsive all at the same time.
I have also recent come to appreciate that you can certainly push Analog and Operator to get some good stuff, but to me the above list will give you a bigger smile and more mileage,
my2c
Using any of these synths will give you better sounds, but for "trance leads" I would suggest starting with a sawtooth wave, and then using the "unison" feature of whatever synth you are using. Unison "copies" the original sound source multiple time and slightly detunes each one. The interaction between these unison voices creates complexity and richness to the tones. If you go really crazy with this, you can for instance take a simply sawtooth wave in Pro-53 by NI and use unison mode with 32 voices, giving you 32 sawtooth waves all slightly detuned around the base note. The result is pretty much the essential base sound for trance leads - and once you understand how this works and why, and play with it a fair bit, you'll have no issue making your own and more original sounding leads.
