As long as you aren't regularly pulling a full load of passengers up hills, I'd recommend the Fiesta 1.25.

I had a newish one for a day whilst my own car was being repaired, and I have to say I was surprised at how nippy it was in town, and how comfortable and competent on the motorway.

Decent ride, smooth engine, and great driving position.

Indeed - often choosing a mid-range model with tyres that aren't too wide and have a profile of at leat 55, and for Fiesta-sized cars of 65-70 over a 45-50 profile will make a huge difference in noise and ride quality, plus having them will help get better traction in snowy conditions when skinny tyres work far better than wide, low profile ones. And, of course, they give increasingly better fuel economy, cost far less to replace, put less strain on the car's suspension (letting the extra air in the tyres do more of the work) and last longer - much better for the cost-conscious driver.

I once used an almost identical car to mine (Mazda3 1.6 petrol) but in TS trim instead of mine in TS2, which meant it had 195/65R15 tyres instead of the 205/55R16s on mine. I definitely noticed a difference in ride comfort, not huge, but enough to convince me never to go for low profile tyres next time around I replace my car. I'm sure driving 100 miles a day 5 days a week would reinforce this view.

I would advise the OP to not go for a high specced car either, i.e. not a 'Ghia' model or suchlike, at least of the non-Japanese models. Higher insurance premiums in addition to the cost price, plus if they go wrong, more costs, and , of course, most of those higher spec models have low profile tyres...better to keep it simple and go for the minimum you actually need (not what you'd like to have).

A also agree about the test drive - go for as long a test drive as possible (an hour would be good - a five minute one round the block is useless and I'd avoid buying from people/dealers who only offer that [you can always offer to pay for the petrol at about £5 for private sellers if you feel brave enough to buy from one]) on a range of roads and speeds, and make sure before setting off you get the seat and steering wheel adjusted as best as possible so as to be able to make the best judgement as you can about how comfortable it will be to drive on a 1.5 - 2.5hr journey to work and to determine if the car has any problems. The OP should also read HJ's 'Advice & Tools' section about buying a car for more tips.

OP needs to do some Insurance research as well. Insurance for 25k a year with no NCB is likely to eye watering at best! If he has been insured on something else without a claim, may be able to persuade an insurer to give an introductory discount against that.

If I were in the OP's shoes I'd be very wary about buying such a cheap diesel-engined car, even from a make (such as Kia) that is generally reliable and it might even be still under warranty for 1 year - its rare for the buyer to know exactly how ALL the previous owners treated (including driving style and annual mileage, especially as before year 3 no mileage is recorded unless you get your hands on service receipts) the car.

Modern diesels are, in my view, far less hardy than petrol-engined equivalents and far more susceptible to problems if they are driven incorrectly (e.g. one year of or regular short trips with only sporadic higher mileage trips that might look ok if you just see the headline annual mileage). As such, at 7+ years old, many major parts may be about to pop and will be very expensive to replace, possibly costing several £000s, and that's before any 'normal' wear and tear items need replacing like clutches, brakes and suspension parts.

Don't forget that the OP has indicated they are seriously considering moving closer to their new workplace if things work out, meaning that they probably wouldn't get much of a fuel saving over each year after they moved, meaning they'd only have (say) 6 months to a year or so worth of fuel savings (less so if they go for a larger diesel car like a Mondeo than with a Fiesta/Polo sized car) but which has the proverbial sword of Damocles hanging over it unless they have 100% of the car's history to hand before they buy.

I agree that for longer journeys, a larger car (with a longer wheelbase) is preferable (all things being equal) for comfort, but as I stated earlier, having the right tyres and comfortable/ergonomic driving position can make just as much of difference.

The citroen c3 is a surprisingly refined motorway cruiser, dirt cheap and cheap to insure.