John,
I mostly develop my own film, but when I use a lab I use The Darkroom UK -
https://www.the-darkroom.co.uk/category/68-colour-negative-film-processing
Two other propular choices are Peak Imaging:
https://www.peak-imaging.com/category/44-35mm-film-processing
and AG Photolab:
https://www.ag-photolab.co.uk/
In terms of "best choice" for a film then the range of responses might end up covering all the choices that are currently available.
Kodak Portra 400 and Portra 160 are very versatile films with a reputation for being able to cope with large variations in exposure - some underexposure and lots of overexposure. They have relatively soft colours.
Kodak Ektar 100 has a more vibrant colour pallette but is more fussy than Portra about getting the right exposure.
Portra and Ektar are rather expensive, although remember that if you are paying for development and scanning, buying a film which is half the price of Portra will not cut your overall bill in half.
Kodak Gold is a little cheaper, and Kodak ColorPlus cheaper again. I'd suggest using one of these options until you're sure that your equipment and technique are fine, before deciding whether you want to use one of the more expensive films.
With regard to your out of date film, then depending upon old it is, and the conditions it's been stored in, there might be some deterioration in the image quality.
XP2 and Fuji Neopan 400 CN Pro are both "chromogenic" films which means they can be processed using the C41 process, the same as the Kodak Gold.
If you're going to be getting your black and white film processed commercially, the XP2 would be a good choice, as the processing will probably be cheaper than a "pure" black and while film (such as FP4+ or HP5+) and it is a high quality product.
Just my two-pennorth to start