Of the two, if you had the money, go for the Stiffi as its much lighter, although also much more expensive. Just remember not to use a fluffy stick
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benjy85pb is right though, I've always only needed .691 and .688 for tiny paint
one or two sizes are usually good enough.
However, I've used Stiffi's, Freaks, Protolites, Ultralites, Fetherlites, Lapcos, Apexes and I have to say the best value for money and all-round performer are the Unitec barrels I was introduced to quite recently.
They are a different system where the back is just the marker adaptor, and the fronts are bored all the way to the end. Thus, if you have a full set of fronts and want to use them on a differently threaded marker, you just need to buy a new back. They are also pretty darn light and come in loads of colours.
Hope this helps.