Water isnt really good with f2p since needs lot of ninjas to work around ( Can work still )
Fire yes its easy to build as F2p player ( Overall easy class to build no matter p2p or f2p lol)
Wind Has same things to water and fire. Easy to build but to make it to other lvl need more ninjas to work around.
Lighting Yes easy to build as f2p same as fire. Lot of free ninjas works.
Earth. I would say not so easy to build. You get ninjas free what are useful to earth but most of them comes so much later lvls compared to other classes ( Well not for water since heck we don't get yet any those fancy ninjas to make us great)

But in overall all classes works both f2p and p2p but all classes needs time to get those ninjas around you to make it work. (Fire is easy road lol )