We spent a couple of nights in Newlyn when we sailed Poole -> Scilly last year. That seemed the best option close to Penzance, as the others (Penzance itself, Mousehole, St Michael's Mount) are all very tide restricted.
All the almanacs/pilots make Newlyn sound dreadful, but we really enjoyed our stay, and found everyone really helpful. Visitor facilities aren't great though - the single shower is only worth using if you are very partial to the smell of fish!
If you don't mind taking the ground, then St. Michael's Mount is a stunning place to stay, and free to boot! But you will be moored against a stone wall...
Other than those, then Falmouth/Helford are probably the next closest ports of departure for Scilly.
The log of our trip to Scilly is here, which might have some information for those first time visitors: http://www.parkstoneyachtclub.com/do...lly%202012.pdf