TBH, I've got to agree with Kyad. An SSD is far and away the best way to improve computing experiences today, period. Processors, RAM, and even graphics cards have now evolved to the point where for the vast majority of users there will be an abundance of power for a rather low price; only high-end gaming, server tasks, and various workstation tasks will require a more expensive product from the above. On the other hand, computers are still handicapped by hard drive read/write times that aren't all that much improved from a decade ago. SSDs can and do cut down boot times by a whole order of magnitude, and make most simple applications (word, web browsers, etc.) boot instantly as opposed to a ~2-5 second lag, which makes for a very noticeably different and much more satisfying user experience. And yeah, for things which do require a lot of loading (like high detail game levels) it will cut down the loading time by an order of magnitude, as well.
TL;DR: SSDs may be expensive, but their added benefit really will improve the overall experience, to a much higher degree than every other component (the next item of importance would be the graphics card, if you're a gamer, but even then you don't need THAT powerful a card to run really any game at this point above medium settings). Hence, it's best to include an SSD even if you have to skimp on other components, simply because it'll be the best value for your money in your daily use.
Also, to the OP, you don't really have to choose between SSD and a hard drive, if you don't want to. You can find super cheap hard drives now anyways, for about $50 for a 500 GB HD. So if you really need to use that much space, it wouldn't cost very much to upgrade