Ola
Também tive bastante problema com o msn, bradesco, real, banco do brasil etc...
Tentei de tudo que tem no forum sobre balanceamento, ai encontrei um tipo de balanceamento no site da mikrotik
Load Balancing Persistent - MikroTik Wiki
Ele deu muito certo aqui pra min, fiz umas adaptações pra funcionar com 4 dsl e uma clientes, numa tacada só resolvi o msn e bancos, so falta ver o detalhe da conectividade social da caixa que não testei ainda, passei entorno de 2 meses pesquisando e testando varias formas, a que mais me agradou foi usando o NTH mas caia muito o msn e banco nem entrava ai consegui este balanceamento alterei pra minha realidade e ficou muito bom, continuo tendo o poder do NTH e o msn ficou estavel e os bancos agora entram
'''/ ip address'''
add address=192.168.0.1/24 network=192.168.0.0 broadcast=192.168.0.255 interface=CLIENTES
add address=192.168.4.253/24 network=192.168.4.0 broadcast=192.168.4.255 interface=DSL1
add address=192.168.2.253/24 network=192.168.2.0 broadcast=192.168.2.255 interface=DSL2
add address=192.168.3.253/24 network=192.168.3.0 broadcast=192.168.3.255 interface=DSL3
add address=192.168.1.253/24 network=192.168.1.0 broadcast=192.168.1.255 interface=DSL4
'''/ ip firewall mangle'''
add chain=prerouting src-address-list=DSL1 in-interface=CLIENTES action=mark-connection \ new-connection-mark=DSL1 passthrough=yes
add chain=prerouting src-address-list=DSL1 in-interface=CLIENTES action=mark-routing \ new-routing-mark=DSL1 passthrough=no
add chain=prerouting src-address-list=DSL2 in-interface=CLIENTES action=mark-connection \ new-connection-mark=DSL2 passthrough=yes
add chain=prerouting src-address-list=DSL2 in-interface=CLIENTES action=mark-routing \ new-routing-mark=DSL2 passthrough=no
add chain=prerouting src-address-list=DSL3 in-interface=CLIENTES action=mark-connection \ new-connection-mark=DSL3 passthrough=yes
add chain=prerouting src-address-list=DSL3 in-interface=CLIENTES action=mark-routing \ new-routing-mark=DSL3 passthrough=no
add chain=prerouting src-address-list=DSL4 in-interface=CLIENTES action=mark-connection \ new-connection-mark=DSL4 passthrough=yes
add chain=prerouting src-address-list=DSL4 in-interface=CLIENTES action=mark-routing \ new-routing-mark=DSL4 passthrough=no
add chain=prerouting in-interface=CLIENTES connection-state=new nth=3,3,0 \ action=mark-connection new-connection-mark=DSL1 passthrough=yes
add chain=prerouting in-interface=CLIENTES action=add-src-to-address-list \ address-list=DSL1 address-list-timeout=1d connection-mark=DSL1 passthrough=yes
add chain=prerouting in-interface=CLIENTES connection-mark=DSL1 action=mark-routing \new-routing-mark=DSL1 passthrough=no
add chain=prerouting in-interface=CLIENTES connection-state=new nth=3,3,1 \ action=mark-connection new-connection-mark=DSL2 passthrough=yes
add chain=prerouting in-interface=CLIENTES action=add-src-to-address-list \address-list=DSL2 address-list-timeout=1d connection-mark=DSL2 passthrough=yes
add chain=prerouting in-interface=CLIENTES connection-mark=DSL2 action=mark-routing \ new-routing-mark=DSL2 passthrough=no
add chain=prerouting in-interface=CLIENTES connection-state=new nth=3,3,2 \ action=mark-connection new-connection-mark=DSL3 passthrough=yes
add chain=prerouting in-interface=CLIENTES action=add-src-to-address-list \address-list=DSL3 address-list-timeout=1d connection-mark=DSL3 passthrough=yes
add chain=prerouting in-interface=CLIENTES connection-mark=DSL3 action=mark-routing \ new-routing-mark=DSL3 passthrough=no
add chain=prerouting in-interface=CLIENTES connection-state=new nth=3,3,3 \ action=mark-connection new-connection-mark=DSL4 passthrough=yes
add chain=prerouting in-interface=CLIENTES action=add-src-to-address-list \address-list=DSL4 address-list-timeout=1d connection-mark=DSL4 passthrough=yes
add chain=prerouting in-interface=CLIENTES connection-mark=DSL4 action=mark-routing \ new-routing-mark=DSL4 passthrough=no
'''/ ip firewall nat'''
add chain=srcnat connection-mark=DSL1 action=src-nat to-addresses=192.168.4.253 \ to-ports=0-65535
add chain=srcnat connection-mark=DSL2 action=src-nat to-addresses=192.168.2.253 \ to-ports=0-65535
add chain=srcnat connection-mark=DSL3 action=src-nat to-addresses=192.168.3.253 \ to-ports=0-65535
add chain=srcnat connection-mark=DSL4 action=src-nat to-addresses=192.168.1.253 \ to-ports=0-65535
'''/ ip route'''
add dst-address=0.0.0.0/0 gateway=192.168.4.254 scope=255 target-scope=10 routing-mark=DSL1
add dst-address=0.0.0.0/0 gateway=192.168.2.254 scope=255 target-scope=10 routing-mark=DSL2
add dst-address=0.0.0.0/0 gateway=192.168.3.254 scope=255 target-scope=10 routing-mark=DSL3
add dst-address=0.0.0.0/0 gateway=192.168.1.254 scope=255 target-scope=10 routing-mark=DSL4
add dst-address=0.0.0.0/0 gateway=192.168.4.254 scope=255 target-scope=10
Espero ter ajudado um pouco, se precisar de alguma explicação fique a vontade pra fazer
abraços