Hi Paul and welcome aboard
You stand to get recommendations for all the engines as there are fans of each on here! Are there any cities in your usual travel patterns which could rule out diesels? If not, I'd recommend a TDI75, they're rather enjoyable with a mild remap. I would say it's generally accepted that this engine and the 1.4 petrol are the more reliable ones, the TDI90 and the FSI are more powerful but have more weaknesses and the FSI in particular is not well understood by most garages. I think there is a 'sweet spot' in the production run in mid-to-late 2002 where they were upgraded with the larger 42L fuel tank but still had the cast suspension arms rather than the later pressed ones, which are prone to corrosion. The earlier variants of the 1.4 engines (AMF diesel, AUA petrol) are also slightly less complex and therefore have less to go wrong than their later counterparts (BHC diesel, BBY petrol).
In terms of model/trim, I'd say avoid the absolute entry level cars, identifiable (if not upgraded via retrofit) by plastic steering wheel, gearknob, handbrake grip and a black rather than silver handbrake button and ring on the bottom of the gear lever shroud. The other trim options were SE and Sport, each of which has their advantages and disadvantages,. Both got leather on the contact points mentioned above. The SE got front foglights and the ingenious false floor, but the seats aren't very supportive for longer drives. The Sport instead got the trip computer and lumbar support in the seats, but the deeper bolsters on these seats do wear and the 17" wheels are less comfortable and prone to buckling. One of the joys of these cars is that there is plenty of knowledge on here to help you to upgrade them yourself with the features that you want, or I'm sure you'll find mention of our resident retrofit guru
@timmus before too long.
In terms of pricing, I'd agree with Bob
@Jellybean, go for history, not mileage, and buy from a forum member if possible. By the nature of an enthusiasts site, these cars stand to have been looked after much more than an elderly part-exchange to clear on a trader's forecourt at the highest markup they can get away with, which is unfortunately all they are to most of the general public.
You should find plenty of information and advice on here and maybe even help from local members to vet prospective purchases. Good luck with your search ? Oh, and I second the motion, pictures of your new pride and joy are mandatory