It also depends on how many internet users you need to support. For a single person, having a 30/30 or even a 50/5 should be more than adequate for the modern web, where you're not going to notice much of any slowdowns. I have 4 very heavy internet users in my household, including myself, and we were consistently choking on Cox's 50/5. To give you an idea, there are 2 people who like their Netflix, 1 person downloading and uploading class assignments (sometimes very large projects), and 1 person who needs ready VPN access to his employer with VOIP capability as well as does a lot of hobby and Open Source development (me). All 4 of us are also heavy gamers both online and offline (almost every Nintendo System and 3 separate X-box 360's in the house, along with at least 1 computer per person, though if I were inclined to share there'd be 2 computers for 3 of us, plus several 'Bones and networked 'duinoes).
For this I went to Cox's second to best tier which was 100/10 (actual speedtests performed to my personal VPS as well as various speed checkers on the web were reporting in the neighborhood of 130/17). This speed was more than adequate for us, but we found ourselves bumping and jumping the 300GB soft limit almost monthly with various game updates and downloads (If we didn't have the gaming addiction we do, we'd have been fine..and no, none of us do the CoD thing, though I'm getting sick of the roommate's Destiny obsession...) so we have moved to the Top Tier which gives 150/25 and a 400GB soft limit (the same speed tests have been averaging at 132/33, though I'm fairly certain it's just the way I have to run the cables in the crawlspace to get signal to every outlet that's causing the download degradation, and right now I'm renting so it's not really worth it for me to re-run new lines. I'm more concerned with increasing the internal wireless bandwidth by adding a dual-band access point as the router is getting overloaded on its single 2.4GHz band channel trying to support all the devices that are trying to get a piece of it).