Diddy, they use both methods for light aircraft. I'd suggest your Cessna 152 would need to be crated, while those with a bit more performance such as Mooneys are flown across usually by professional ferry pilots, via Greenland and Iceland (northern route) or the Azores (southern route). They may well need ferry tanks to have sufficient range. Twins and bizjets are all flown across I think. It does carry a risk and pilots are occasionally lost.
I heard of one Luscombe that was ferried as far as Narsarssuaq before weather defeated the plan, and the aircraft was shipped onwards. Luscombes and similar antiques arrived in droves three at a time in 40ft containers during the 1980s.
Somebody (Torquil Norman?) recently flew a Leopard Moth across to the USA, and some warbirds are flown across, such as the P-51D Miss Velma that arrived here last summer.