Php 5.6 or 7

PHP 7 was benchmarked to be twice as fast as 5.6 in specific cases. I would also update regardless as staying behind is only likely to become a negative in the future.

PHP 5.6's EOL is in 2018 (December 31st)

PHP7 is several times faster than 5.x, all hosts should be making the switch or have the option for 7, if said host does not have it, i suggest you move to a different one.

The only reason I would suggest staying on 5.6 would be the software doesn't yet support 7.x, other than that you should certainly be looking into migrating over to 7.x

Yes, unless you are supporting and old platform based on an old PHP version that can't easily be modified and what you are trying to do can actually be done with the latest version I don't see a reason for holding back.

PHP 7 ofcourse .... i had no problem

php 7, much more security. ))))

Php 7.1 because is faster than older versions, but depends on the cms that you are going to use/or use.

for new php-based project, 7.x - your choice. but don't forget about ioncube_loader if you want to use one

if you gonna study use latest php ver.
But if you gonna write stuff for sale use lowest ver. 5.3(2)
Most of hosters use 5.3 - 5.6