It's a personal opinion matter. Myself, I'm partial to spades, but right now are using bare wire for my 2-chanel rig and flex-pins for my HT rig. Once I get my 2-channel's placement finalized, I am going to invest in some spades and make some nice cables.
Here is my opinion on each
solid pins: worthless, contact is too small
flex pins: far better than solid, similar contact as bare wire, but fits in spring terminals.
bananas: similar contact to flex pins, but easier to use, just push into the top part of the binding post and your good to go.
spades: huge contact area, but only a handful of equipment will handle them. (I had to modify my Yamaha RX-496 to accept spades).
Really, just go with what you like, but I do strongly advise against solid pins...the contact on them is very poor since the pin is so thin and doesn't flatten out.