Anything with an Ivy bridge processor will be a vast improvement, coupled with 6-8Gb RAM and a SSD of reasonable size. Its then a matter of how big a screen you want to lug round and "looks". If weight is an issue look at what are termed "Ultrabooks".
There aren't many people with huge experience of lots of different laptops to provide a balanced view of the pros/cons, tech review sites are the way forward.