I've often wondered that too. At the end it comes down to personal choice - they are both relatively good cars. Contrary to perceived wisdom, many reliability surveys place the European-built Focus much higher than the Golf. Also I have read that the Focus is supposed to handle better than the Golf. However the Golf does have higher perceived quality - i.e. softer touch, less shiny materials in the interior.
You should take them both for a test drive, as ultimately it is you driving the car not us
If you are driving 50 miles a day then a diesel car will help keep fuel costs down, and have lower emissions than petrol cars. For me, I would rule out a 2006 1.9tdi Golf as it will cost 582 in car tax a year, as opposed to 104 for a 2008 focus. But if you prefer the higher powered cars, then the Golf 1.9 might be the better option (although 1.8 diesel focus also available). I have driven a 1.4 petrol Golf, and a 2009 diesel focus zetec, and found that I preferred the focus.
FYI – Car tax rates….
The rates of Irish Car Tax from January 2010 are shown below based on CO2 emissions
Band A: cars that produce 0-120g/km CO2 - €104 road tax;
Band B: cars that produce 121g - 140g/km CO2 - €156 road tax;
Band C: cars that produce 141g-155g/km CO2 - €302 road tax;
Band D: cars that produce 156g-170g/km CO2 - €447 road tax;
Band E: cars that produce 171g-190g/km CO2 - €630 road tax;
Band F: cars that produce 191g-225g/km CO2 - €1,050 road tax;
Band G: cars that produce 226g/km CO2 and over - €2,100 road tax
The difference between the lowest and highest car tax is €1900 a year - quite a substantial saving.
Older cars registered before July 2008 will continue to be have motor tax based on the size of their engine - the bigger the engine cc - the higher the tax.
Listed below are the car tax rates in Ireland as at Jan 2010 for cars registered prior to July 2008.
The amounts can be paid for 6 months or 3 months - but the rates are slightly higher than if you pay for a full 12 months.
Engine Size --- Annual Car Tax in € Euro
Not over 1,000 cc - €172
1,001 to 1,100 cc - €259
1,101 to 1,200 cc - €286
1,201 to 1,300 cc - €310
1,301 to 1,400 cc - €333
1,401 to 1,500 cc - €357
1,501 to 1,600 cc - €445
1,601 to 1,700 cc - €471
1,701 to 1,800 cc - €551
1,801 to 1,900 cc - €582
1,901 to 2,000 cc - €614
2,001 to 2,100 cc - €784
2,101 to 2,200 cc - €823
2,201 to 2,300 cc - €860
2,301 to 2,400 cc - €895
2,401 to 2,500 cc - €935
2,501 to 2,600 cc - €1120
2,601 to 2,700 cc - €1164
2,701 to 2,800 cc - €1204
2,801 to 2,900 cc - €1,248
2,901 to 3,000 cc - €1,293
3,001 or more cc - €1,566