Question re: iMac purchase for Parallels

Hello, thanks in advance for your help! I am going to be purchasing a 21.5" iMac and will be using Parallels on it quite frequently. I wasn't sure if my best bet is to purchase a fusion drive (1TB) or an SSD drive (256 GIG). Im not in need of a lot of space on my computer as the files we will be using are mostly QuickBooks files, but i wanted to get your input as to which option you think might be best in terms of getting maximum performance from Parallels. Thanks very much for helping me. I do not mind using external storage for our files. take care, rick