Linux – Are balance-xor and 802.3ad modes of Bonding meant to provide per-flow balancing

I'm not terribly familiar with Juniper switches, but you shouldn't have to configure LACP on them; that is the point of LACP. If this isn't the case, something is wrong with your switch configuration.

LACP only specifies a protocol for dynamically aggregating ports. It does not specify a port scheduling policy (where traffic is sent and received). This policy is set separately. I don't remember the process in Linux, but I know Linux supports specifying at couple different policies, probably similar to balance-alb.

The balance-alb has specific disadvantages. Mainly that it semi-intelligently selects an outgoing port for new connections, and they're stuck to that one port for the life of the connection (it's actually done by MAC, not port, if a port fails the MAC gets assigned to another port, thus allowing the connection to continue).

This doesn't exactly "aggregate" the ports however, as connections will not be able to utilize more than one port. So if you've got 2 1GbE ports, a single connection is still limited to 1GbE. LACP resolves this usually, though it depends on your scheduling policy and the number of active ports supported at each end.

From this page regarding balance-rr:

This mode is the only mode that will permit a single TCP/IP connection to stripe traffic across multiple interfaces. It is therefore the only mode that will allow a single TCP/IP stream to utilize more than one interface's worth of throughput. This comes at a cost, however: the striping often results in peer systems receiving packets out of order, causing TCP/IP's congestion control system to kick in, often by retransmitting segments.

And regarding 802.3ad:

The 802.3ad standard also mandates that frames be delivered in order (within certain limits), so in general single connections will not see misordering of packets.

So 802.3ad provides better ordering of packets which avoids TCP retransmissions.