You're not going to find many reasons beyond cost-saving for a 1.4 over an S3 as really, the S3 is an engine upgrade when you really get down to it. The only other area I guess of difference is around ride which would be somewhat harder on the S3 than the A3, and this is very much a thing of personal preference. If you like a more supple ride then the A3 SE would be your best bet.
Personally (of course because I've ordered an S3), I'd suggest its a great choice, but I'm not so parochial to assume that just because I think something is right for me, everyone else should agree. I'd personally really think about what is important about your next car. It sounds like you're coming from a much older car, so the standard A3 will be a massive jump up, you'll get the same lovely interior, ride quality and sophistication, and premium badge. If you really want a performance car, all the extra bling (not that much really but you know what I mean) that comes with an S3, then perhaps it is for you.
The S3 will always win a lot of battles againt the A3 as it is the top spec car (currently) in the range, so you're always going to get a lot of advocates on here for that (it the same way that all audio threads end up with people suggesting you go for B&O!), but I'd give it due thoughts on what is important about your car.
Just my 2p
Personally (of course because I've ordered an S3), I'd suggest its a great choice, but I'm not so parochial to assume that just because I think something is right for me, everyone else should agree. I'd personally really think about what is important about your next car. It sounds like you're coming from a much older car, so the standard A3 will be a massive jump up, you'll get the same lovely interior, ride quality and sophistication, and premium badge. If you really want a performance car, all the extra bling (not that much really but you know what I mean) that comes with an S3, then perhaps it is for you.
The S3 will always win a lot of battles againt the A3 as it is the top spec car (currently) in the range, so you're always going to get a lot of advocates on here for that (it the same way that all audio threads end up with people suggesting you go for B&O!), but I'd give it due thoughts on what is important about your car.
Just my 2p