What, besides the price is the difference between unmanaged, smart, and managed switches? Why would I choose one over the other?
Managed Switch Vs. Unmanaged Switch
managed switches, mainly features like VLANs, Port Mirroring, SNMP, adjusting the port speed
Most managed switches offer you features like:---View the bridging table to see which MAC addresses are associated with a given port
---View error statistics for each port
---View packet transmit / receive statistics for each port
---Set duplex / speed negotiation (or lack thereof) on a per-port basis
---View power-over-Ethernet status and current draw for each port (if applicable)
---support things like 802.1D spanning tree, 802.1q VLANs, and 802.3ad link aggregation,
---setup port VLAN memberships, link aggregation groups, and control spanning tree parameters all from a web or command-line interface
Typically there is a TELNET, serial, and / or web-based interface to interact with the switch.Many managed switches allow you to poll the device with the SNMP protocol to use the information described above in graphs, alerts, etc..Some managed switches are to emulating the Cisco command-line interface (HP ProCurve, Dell PowerConnect....) such that someone with Cisco-specific knowledge can easily configure those switches.
Unmanaged switches have a set of basic features but no options for configurations. They just work they way they do ~ plug&play.
Managed switches have a load of features and allow full configuration via CLI (command line instructions) and in most cases offer also a web interface to easily configure the most options. In addition to the (almost) standard SFP ports for up-linking they are mostly stackable (not going to explain because this already is long enough, see Wikipedia)
Smart Managed switches are somewhere in between. They have more features as unmanaged switches but only allow a certain amount of individual configuration via web interface (in most cases they don't offer a CLI).
Unmanaged switches are primarily targeted for home and SOHO; Smart-Managed switches are mostly for small to medium sized business users who may need some or certain configurations; fully managed or enterprise switches are for large business, high-traffic applications e.g. data centers and other applications where you need either or all things like maximum configuration, centralized management and monitoring, speed and performance.
As for choosing one it's mostly about two things: Budget and application. If you just want to setup a network unmanaged or smart-managed switches are good enough. If you need configuration options like like VLAN, QoS you will have to use a smart-managed or managed switch (depending on the features they offer).
For high load networks or time critical applications with a lot of traffic I would say smart-managed is the minimum simply because most unmanaged switches are kind of "trimmed down" in terms of backplane an switching speed ~ they don't have the bus and port-to-port switching speed to handle high traffic in a timely manner.