My favorite used to be Kodachrome. When Kodak stopped doing any process-paid slide film I moved to Fuji (Sensia usually), because they were the last company to offer process paid slide film in the UK. But even that ended a few years ago. Now I buy recently-expired stuff off ebay; I just use whatever's listed at the time I need it. I can't avoid my wallet being raped for the processing unless I process my own (and I have neither time nor space) so any opportunity to save on the price of the film itself I'll jump at.