I have a Mk 1 Octavia estate (so probably a bit older than you are looking for) and it is reliable, despite it having the known-to-be- ridiculous AQY engine (2 litre 8v) and there has been issues with it, most significantly the check engine light has been on for the best part of a decade and despite several investigations, nothing has cured it. But the fuel consumption has been fine, emissions are fine, all is fine, basically.
I previously had an Octavia with the 1.6 8v engine which never had any problems.
I think the newer Octavias with an engine other than the AQY would see you right.
My father has an '08 Mondeo and it is superb. It is a very big car though, but the 2 litre TD engine and the 6 speed autobox are a magic combo!
Both cars are easy to deal with regarding bulbs, etc. The only downside of the Mondeo is that to do an oil change, you have to remove the under-engine tray, but really, it's no big deal. Mondeo also has a great stereo, whereas the Octavia's is a bit anaemic. Mondeo is incredible on long journeys, quiet and smooth and very roomy (I am 2 metres tall)
The one thing I would say to look out for on any car you choose is:
Try to avoid low profile tyres, they are a bit of a nightmare in my experience. I like cars to be smooth and comfortable, but the stretched elastic bands on 18 inch wheels the Mondeo have do not make for as smooth a ride as smaller wheels & higher profile tyres would. The Octavia has
15 inch wheels and higher profile tyres and soak up bumps a lot better than the Mondeo, but the Mondeo has a
/smoother/ ride over all. If it had the h/p tyres, I think it would be pretty much perfect!
Neighbour is a taxi driver and has an '06 E class Mercedes 2.7 diesel. He loves it, but he is fairly short and I found it much too small headroom-wise for any sort of distance driving. Other than that it's pretty good. Problems he has had with it (all electrical) were traced to a faulty voltage reg (iirc) on the alternator. Once this was swapped (he actually had the whole alternator done for sake of time), problems disappeared. This car has two batteries, one in the boot, a smaller one under the bonnet. The Merc also has 18 inch low profile tyres, but the suspension must be made from magic as it soaks up bumps better than the Mondeo. He had the engine serviced last month, inc. all fluids & autobox oil, a shade over 400 quid from the main dealers. He thought it was a bit steep but they did it very quickly - time is money for him concerning the car, so he paid it due to the turnaround).
My order of preference would be:
- Octavia (keep in mind mine is the Mk 1 and I have no experience living with newer models) due to large interior for driver, colossal boot, put the rear seats down (or remove them) and you've got a large, long load space. My dickie engined one (petrol / manual box) will do
50-ish MPG at 60-ish on a motorway run. Older car, cheap parts, very easy DIY. Narrower body than the Mondeo, and good visibility from driver's seat makes parking very easy.
- Mondeo. All the luxuries (Titanium X spec) loads of passenger room in front and back (serious amount of rear legroom). 2 litre turbo diesel (auto slushbox i.e. not DSG type thing) at "motorway speeds, officer" motorway run will return 50-ish MPG. Parking radars very useful. Still a massive vehicle though.
- Merc. Too small for me to realistically live with, no other experience with it but it must be durable to keep a taxi driver happy. No idea about running costs other than example given. Looks nice, I suppose.
And that's all the experience I have. Hope it can help in some small way.