In case your website is dynamic (like blogs), then you would need an unlimited hosting package.
All unlimited shared hosting packages come with what will ultimately prove to be quite limited CPU/memory/inodes allowances. A dynamic site is much more CPU/memory intensive than a static one, so they will reach these limitations faster. The main advantage of an unlimited space and bandwidth account is the implied guarantee that you're not going to be charged for using "a lot". I recall some horror stories where bandwidth or space usage beyond one's quota was charged at a very high rate, and people who had bought $6/month shared hosting suddenly found themselves charged $1000 or more in over-usage fees.
No single hosting provider can provide 100% up-time.
Absolutely correct. Still, an uptime guarantee is generally not worth the money. Would a day of downtime really be that much better if you got your monthly fee of $6-8 refunded? For most of us, not really, no.