I was in the same position as you, a 19 year old Merchant Navy Cadet with a PPL, who was torn between the two careers. I did not go with CTC at the time because as you say my MN training was being paid for, and I would have needed a large bond with no fallback with CTC.
Long story short I am now 30 year old Master Unlimited who has just assumed command of my first ship.
With the benefit of some experience I would say this:
As an airline pilot there is a lot of time spent in the cruise monitoring systems, with high levels of automation. When I was a navigator on cruise ships, I spent 8 hours a day monitoring the radar, ECDIS, IAMCS etc. Pretty dull. But there less automation at sea. In fact when I am in a particularly enthusiastic mood I dig my sextant out and navigate with the stars.
Despite this I find the shiphandling a lot more of a challenge than flying, although granted I have only flown light aircraft. Trying to handle a large ship with a strong tide, in strong winds, into an awkward berth is very exhilarating. Every port is different with different challenges and it is a lot less prescriptive than flying. I find there is more going on in berthing a ship than flying an approach procedure 'by the numbers'.
There is nothing glamorous about inspecting a grey water tank as a chief mate, or getting covered in grease whilst fixing a lifeboat as 3rd mate - but it adds a practical dynamic that you won't get as a pilot - it depends on your character. If you want to stay in the warm and dry all day and not get dirty, then the flight deck is probably more your cup of tea than the weather deck; nothing wrong in that at all.
Both industries are cyclical - try getting a job at sea at the moment, its tough. But you will get one in the end.
It is hard competing against workforces from the far east, you will know that the vast majority of ships crews are Filipino, Indian, Russian etc. As someone from Western Europe you will really only find work on specialist ships. That said I have worked on cruise ships, expeditionary ships, ferries, square rigged sailing ships, cargo ships. There is a lot more variety at sea than in the air. Working on a cruise ship is a lot different than working on a dredger - compare that with transferring between an A320 and a 777.
As a class 1 Master you have a huge number of options: Stay at sea, go into the MCA, MAIB, lecturer, Port Ops, Ship Ops, Law, Insurance, Chartering, etc etc. All of my class mates have very successful careers. I also do a bit of moonlighting as an STCW trainer. It is a lot more diverse.
The major downside to staying at sea is the time away - 4 month trips are long. That said the standard contract for a Brit now is 1:1, and I do 4 weeks on 4 weeks off. This is much better, I find, than my friend who is a pilot and whose roster is constantly changing and has all sorts of different shifts.
Seafarers can be treated very poorly in comparison to pilots, especially when things go wrong. Look at the way the BA crew at Heathrow or the US Air crew in the Hudson were treated and compare that with shipping (Costa Concordia doesn't count he didn't exactly shower himself in glory). Standard practice is to arrest the Master after an incident.
I would consider getting your CoC, do a couple of runs as a 3/O to get a few stamps in your book and get some tax free £'s in your bank. At least then you can make more of an informed decision, have a fallback career and if you do decide to go on an airline scheme you'll have some cash to get you by (accommodation, car, food etc).
I know of pilots that are happy, some not. I have colleagues that are happy, some not. Just look at the long term, because whatever you choose at the end of the day it becomes a job of work that will need to support you (and your family if you have one).
Just some thoughts for you; if you have any questions just ask.
Cheers,
Richard