Personally, I'm a huge fan of pitch-strips when it comes to vibrato. Rocking your finger back and forth can give a VERY natural vibrato, far better than some mechanical delayed LFO with a fixed period. Let's face it, if you spring for the ultimate in realism by going the software route, why ruin it by using a mechanical vibrato?
If you absolutely HAVE to have a hands-free delayed vibrato (because both your hands are tied up), at the very least, try to modulate the LFO 'speed' as well as depth... Most real instrument players will speed up the vibrato as it gets deeper, and slow it down on just slight touches. Program the LFO to be a bit slower than you would like, and use an envelope (if you are doing this hands free) to ramp up the speed to slightly faster than you like over time. This can help at least get away from the static nature of most arranger vibratos, that have no modulation of speed at all...
Hope this helps.
[This message has been edited by Diki (edited 06-08-2008).]