One would argue that the md3000 isn't a true SAN, but simply shared DAS. In some cases, DAS can be faster than iSCSI depending on connectivity options, but is more limited in the number of hosts it can support (even more so when trying to have redundant paths to the storage) compared to iSCSi connectivity. the MD3000 will likely require an external SAS HBA to be purchased as well, the 3000i may require additional NIC's and/or switching gear depending on your current infrastructure.
All this being said, you haven't really told us what your needs on the DB's as well as the web servers connected to it (expected IOPS, read/write ratio, expected RAID settings, etc) along with the current/expected usage of the other servers you are planning on connecting and desired level of redundancy, etc.. From your general description, either would be probably be fine from a performance perspective but with 4 hosts, the MD3000 will only allow a single path to the storage. the 3000i could allow you to setup MPIO with iSCSi (assuming you have the appropriate number of NIC's and switching).
This also borders on a "what do I buy" type of question which is generally frowned upon here.
Is there a reason you are set on only those two options?