I am not expert so I can say only what I know or what I think I know...
WDS http://www.mikrotik.com/testdocs/ros/3. ... nt.php#.11
+ allow transparent communication between multiple ap on same channel with same essid and so allow to extend signal coverage
- needed to enter MAC address of opposite side wlan card on ap to new wds interface for each wds peer (ap-bridge, bridge, wds-slave, ...)
+ it is decentralized or distributed, ap which cant see each other can communicate through ap between them
* it is usable only on wireless interface
- maybe packing ip packets have more overheads than wds communication (somebody can make exact measurement or calculation)
+ as tunnel it can be used between any ip address across Internet and over multiple hops
+ more instances can be create between same pair of address with different tunnel id.
* tunnel is only Point-to-Point but more such links can be bridged together.
- tunnel need to have different IP addresses (if used) than physical link so both sides of tunnel have to be reachable over another ip subnet (more complexity)
For both it is necessary to create some new virtual device wds or eoip1 and make bridge to some other physical interface.
I am using only WDS bridge right now but I useded eoip tunnel to access from home to all subnets on network. Thanks to ethernet tunnel my computer was connected directly to remote subnet and get ip address from local DHCP and i was able to connect to hosts which have restricted access only from local subnet.
Somebody has mentioned that WDS was working somehow bad with routeros 4.x beta on 802.11n link and suggested EoIP tunnel as another solution for MAC bridge on client-ap or ad-hoc link.
So it's good to have two different methods to overcome wifi ap-client limitation.