Paradoxically, the speeds that I'm getting from my rMBP13 for SMB transfers are comparable over Ethernet (both Apple Thunderbolt adapter and rangom assortment of TB2 docks) to Linux and Windows machines, but over Wi-Fi, rMBP is much faster than any Linux or Windows machine I have. The Mac machine is 802.11ac 3x3 MIMO by Broadcom, while the others are only 2x2 by Intel, but I'm not sure that the speed difference could be explained just by this factor.
Yes, there were small bugs in the past, like waiting for some timeout when browsing shares on the server when the auth is done via Kerberos, but they were ultimately fixed.