
Last summer I took my Wild Country Levache (4.8kg) to Italy with Ryanair.
http://www.summits.co.uk/acatalog/Wild_Country_Levache.html
(first result on a Google search)
TENT
I previously had a Eurohike tunnel tent that was the same shape, but quite 'wobbly' in wind - I liked the fact that the porch is as big as the inner (which is big enough for 3).
The Levache has two points where the poles cross, leading to greater resistance to wind and less general flapping about.
The large porch means that it isn't cramped if you have to cook and spend the evening in there in bad weather.
FLIGHT
Ryanair do still allow 25kg per person, but you have to be canny in splitting it between your hand and checked baggage (10 and 15kg respectively). What we tend to do is wear our heaviest shoes & clothes (coats included, no matter how warm it is) as they don't actually weigh YOU (yet...), stuff our hand baggage as full as possible and then put the remaining equipment in the suitcase.
Also, if you take water on the flight, don't put it in any of the bags (it's 1kg per litre) - just try to hold it as inconspicuously as possible.
CAR
With regard to your comment about car hire, bear in mind Ryanair's 'relaxed' attitude to airport locations. You may find that you spend nearly as much money (and a lot more effort) getting from the airport to the nearest public transport hub and then on to where you want to go, than just hiring a car.
Also - and this only applies to our experience in Italy - it is a car culture, and the corresponding lack of public transport would have made it very difficult to get to the places we wanted to stay.
AND FINALLY
Back to the tent to finish - I think you need to decide what you want to use the tent for. If you are mainly going to be carrying it around, and just putting it up in a corner to sleep in, then the lighter ones (Coleman, Jamet) would be better. However, if you are going to be pitching it for a few days in a proper campsite, you may as well go for the extra kilograms and get lots of space, so that you can spread out and relax more.
Hope this helps,
Mark.