Firstly:
I've come from driving Passats and A3's to my first 3 (barring a couple of weeks with an E36 325i a few years ago) - I can safely say that short of suddenly being able to run an RS6, I won't be going back.
As for which engine - personally I would go with the 330d. The petrol will be more fun (it's just something about beniog able to rev further and the nicer sound), but the diesel for everything apart from 0-60 will be quicker. A chipped 320d will keep up with a 330i without much cause for concern, and it'll be using a darn sight less fuel. However, as you have noted, the petrols are MUCH cheaper. I know of someone who had a 330ci cab on a 54 plate on his forecourt for most of the summer with a price tag around half what I paid for my 03 320d from a main dealer and it just wouldn't sell.
Secondly, I've got to address this following point:
cheers lads. I absolutely hate changing gear - I want to be able to relax, but still be able to give it some if and when the opportunity arises. I really dont see why people get so hung up on manuals!
Why does it make a better drive? Seems to me not having to change gear yourself is one less thing to have to do in addition to concentrating on the road. It doesnt make you feel more involved, just gives you more to do, like if we had to hand-signal cos indicators were for lazy drivers.....driving isn't a job for me, its a pastime, but a lot of the time its a chore
I've had a couple of autos and a VAG tiptronic, and I really started to miss changing gear myself - the vag tiptronic box was rubbish (designed by porsche, it was mechanically superb, but the software ruined it).
I can see where you're coming from - being able to overtake by just pressing down on the throttle and having the car take off is great. As is the feeling of relentless acceleration you get with a smooth changing auto on a powerful box.
Personally though - sometimes I just want that feeling of hammering up through a couple of gears when I'm accelerating. There's something satisfying about grabbing hitting the clutch and slotting the lever into the next slot. Especially when you get it just right.
I don't know if you drive on track, or spiritedly take the car down twisties etc, but allow me to give a couple of examples (out of many) where you can do things with a manual that an auto (and a badly softwared semi audo) would ruin:
Getting the back end out-
you come to the apex of a slow bend in a low gear at low-medium revs, and hoof it.
Manual Box- you can hold the back end out as you exit the corner and use the higher revs to gain speed along the straight - or retain the same gear for the next corner.
Auto Box- the back end will step out as with the manual box, it will then hit its shift point, change gear, and kill everything. Wrong gear for accelerating, wrong gear for following bend.
Rather specific, but as I say, just an example (and there are plenty of instances of this very corner out there)-
The "down hill into fast mid-gear bend into uphill gradient":
Manual Box - approaching the corner in mid 4th, you blip the throttle and
shift down to 3rd, hold revs round the bend and accelerate up the hill.
Auto Box - approaching the corner in mid 4th, you hold mid-low revs in 4th around the corner, then either bog down or change gear mid corner as you apply the throttle when the car starts to slow.
..by which time the manual car will be halfway up the hill.
It's just more "fun".
A well set up tiptronic is a nice compromise between the two, and of course means no clutch replacements!
Don't forget also that auto boxes create a bigger transmission loss, so it'll use more fuel and be slightly slower in gear than the manual version. Can't quote for the BMW, but the VAG tiptronic box from early 2000's (the version before the DSG) used 15% more fuel (yes, really) and sucked up about 10-15% of the power output (it made the chipped 115bhp passat feel about the same as my previous 110bhp manual before it was chipped, after, chipping, the 115 wouldn't know which way the 110 had gone).
Newer ones are better, we had a 52 plate 530i sport (fab car) and the semi auto on that was very good.
Hope some of this makes sense!!
Have to say though - autos and semi autos are fabulous if you spend any time in traffic.
End of the day, it's not for me to defend manuals against autos, it's down to driver preference. A manual will always offer more control than an auto (with the possible exception of the ferraris and lambos of this world) but if you can live without the 10% extra feel for 10% of the time, then may as well go semi.