On some cruise lines you can guarantee a minimum category - so on Princess you can book not just any balcony but a Cat BE (for example). That way you will not end up in a lower category and have that obstructed balcony. Certainly study your deck plan before booking a a guarantee. We did a BG guarantee on Ruby Princess because there are no obstructed balconies.
All I ask is a tall ship and a star to steer her by; John Masefield
Carnival: Glory 2004, Destiny 2008, Splendor 2009, Freedom 2011, Valor 2012, Dream 2013
Celebrity: Summit 2011
Princess: Ruby 2010, 2014, Caribbean 2013, Coral 2014, Regal 2014
Star Clippers: Royal Clipper 2015