Caravanning Now

Directional (Freeview)

Pros:

Very strong signal that does not (usually) require amplification.
Unlikely to get on-screen ghosting.
Will work in poor reception areas.
Possibly built in FM or DAB radio aerial.

Cons:

Needs to be 'aimed' at the transmitter.
Needs to be twisted to provide the correct signal orientation (Vertical / Horizontal).
(Usually) Can not be left attached to the caravan while on the move.
Doesn't require a decoder box.
Will only work in Europe if you have the correct type of television receiver.

Examples of:

Most probably the aerial you have at home (assuming it's roof / gutter / loft mounted)
For orientation instructions see www.wolfbane.com/cgi-bin/tvd.exe.

Omnidirectional (Freeview)

Pros:

Can be left permanently attached to the caravan.
Never needs to be aimed.
Usually has built in FM Radio aerial.

Cons:

Poor signal (always needs amplification).
Requires a good strong signal to produce a good image.
Suffers from ghosting.
Will only work satisfactorily in a 'good' reception area.
Doesn't require a decoder box
Will only work in Europe if you have the correct type of television receiver.

Examples of:

Status which looks like a (small) flying saucer. It might have a radio aerial mounted from it's centre.
Omnimax, which looks like an arrangement of wires formed around a large jam jar.

Digital Satellite Dishes (Sky / Freesat)

Pros:

You can use the same aerial / TV almost anywhere in Europe to pick up English language broadcasts.
Will work nearly in Europe with a clear view of the south-eastern sky. (For satellite coverage see users.powernet.co.uk/hack/astra/).

Cons:

Requires a decoder box and a decryption card to work. ('Free to air' programs on Sky can be picked up with a free decryption card.
Can take a long time to set up and to aim at the correct geostationary satellite (requires a compass and practice).
Taking your home decoder box might break your digital satellite agreement.

Examples of:

The standard digital Sky or Freesat dish as (frequently) bolted to a wall near you.
If you have a digital setup at home, then it may be possible, after your 1st year with Sky, which requires you to have your decoder attached to a phone line, to take your decoder with you and to use a second hand dish. Ground mounts and mounts that are attachable to your van are available, I'm told.
For instructions on fitting and aligning satellite dishes when caravanning see David Sullivans excellant site www.satelliteforcaravans.co.uk/.
The site users.powernet.co.uk/hack/astra/ has the Astra 2 beam "footprint" maps.