Here's a little prespective from a painter who has stained homes and deck's from Maine to the Rocky Mountain's. I take pride in my work and would much rather see something done right than done wrong or not even done at all, whether I get the contract or not.
Deck's: Stain your deck(s) 1 time, each year for 3 years, then it's ok to stain it every 3rd year. Alot of people believe that 1 application of deck stain will last for years...99% of the time it won't.
This is how I prepare and finish decks that have failing stain:
I like to use Sherwinn Williams Deckscapes stripper....on all horizontal surfaces, handrails and the flooring. I then take palm sanders and go over all areas that have been stripped to remove any existing finish that didnt come up and to smooth the wood.
An application of bleach ( Sherwinn Williams Deckscapes Revive ) is applied and then rinsed off. Allow proper drying time and then apply stain......BRUSH, BRUSH, BRUSH.....the more you work it in the better. I wont recommened a stain (unless you ask) but a semi transparent or semi solid stain is along the lines of my use. NOW..... what about all the vertical material? If your keeping a similar color than there should be no problem using a semi trans or semi solid, but if it is a color change, I like to do all the vertical material with a solid stain, it gives a contrast, 2 tone apperance and looks great. If you would like to spend the extra time (sanding each spindal and all vertical) and money (more stripper and bleach) to do all the vertical materials then feel free but this is extremley cost effective and a great looking way to refinnish your deck(s) the right way. Any question's feel free to get ahold of me.
I recommend the S.W. product for stripping and bleaching because they work great on any product that is on the deck to remove it.