I don't think there's a correct answer... The answer is "it depends." It depends on the song, it depends on the genera, it depends on the mix, "it depends..." 
 
Why not have several? :-) 

Firstly thanks for all the replies, as ever the generosity of the people on this forum is fabulous!
 
I have downloaded demos of Saturn, Wavearts tube saturator and then the few freebies mentioned as well. Decapitator is giving me some install issues though.
 
After a couple of days on different sources none of them are really bad it just seems to be about value for money and options.
So far I do like Saturn the choices of distortion are great and the bands plus the modulation possibilities look interesting as well. It also has the options for doing subtle which is good and something I was really looking for. Clean tube especially offers control at lower levels that I have not found in other plugs. Looks like I will have to start saving for this next!
 
IVGI was nice for free and the big brother does look like it could be a good one as well.
 
I already had Redopter and this caused me to look at it a bit deeper and compare to the others it does hold up quite well and I feel better about my purchase now I have explored it some more. Then I just need to get decapitator to work now to compare it to Saturn.
 
Bit what settings are you tending to use on vocals? Also do you use effect on the channel or on a bus?
 
Thanks

I've used Saturn on both individual tracks and busses. I do like to use it differently on foreground versus background vocals, though, so a common vocal bus usually won't be a good place for it.
 
I usually use two bands for BGVs and three bands for lead vox. For BGVs I like the glassy sheen of the tape modes, but for leads I'll more often go for one of the tube modes in the midrange band and tape modes for the high and low bands.
 
Don't overlook the "Dynamics" knob, especially on background vocals. They've hidden a simple but effective compressor/expander in that plugin!