I have the choice of SSD or HDD for my upcoming hosting change. Do I really need SSD? It cuts my available space in half so I'd like to use HDD instead. Will I notice any difference on a forum with no more than 7 or 8 members on-line at once (and NO bots or guests)?
We moved from HDD to SSD 2 and a half months back, the performance improvement was visible. Things function a lot more fluid and smoothly, cannot pinpoint anything in particular but we have certain days (2 days a week) where there is heavy traffic (3000+ guests constantly for over 15/16 hours) and a lot of members online (more than other days) who post and interact with content (like, report etc.) a lot. We got our server optimized by @MattW and it functions very well, but the move to a SSD plan made even greater difference for us (well, that and adding 2GB additional RAM...).
Generally, I'd recommend an SSD as it can't hurt to have one. If budget is an issue, the best way to look at it would be: Do you actually need the extra space?
Sure, having 20 GB space might sound more attractive than just 10 GB, but the average website is only a few hundred MB large. In this case, it makes sense to cut the extra HDD space and opt for an SSD. If this is reversed however, then opt for a HDD.