dhcpcd only features

• DHCP over FireWire
• User Class
• SIP Servers
• Domain Search
• Classless Static Routes
• DHCP over InfiniBand
• TimeZone options
• IPv6 Router Soliciation including optional address and route management
• SixRD
• UUID-Based DHCP Unique Identifier
• IPv6 Stable Private Addresses
• Seamless quad stack of DHCPv4, IPv4LL, IPv6RS, DHCPv6
• Wireless SSID profile support
• ARP ping profile support
• Dynamic route management for systems without metrics (ie, the BSDs)
• Share same IP address across different interfaces (only one active though)
• Exposes interface events and properties via user configurable shell scripts, sockets and libdhcpcd
• Support for dynamic /dev managers who like to rename interface (ie udev)
• Small runtime, 220k on amd64 NetBSD

Features shared with other clients (not just DHCP)

• Link carrier detection
• Prefix Delegation
• Node-specific Client Identifiers
• IPv4LL, APIPA or ZeroConf
• IPv6 Router Advertisement Options for DNS Configuration

It should be noted that FreeBSD and several Linux distributions ship ISC dhclient with patches to enable Classless Static Routes.