Hi Phil,

Transaction replication with updatable subscriptions allows subscribers to
make local changes, which is then propagated back to publisher using
two-phase commit via MSDTC.  Merge replication on the other-hand is designed
for solutions where the subscriber may not always be "connected" and any
local changes are stored locally until they connect and changes can be
propagated to publisher.

Transactional replication with updateable subscribers is really for a
"conntected" subscriber.

Thanks,
Phillip Cox

There are two forms of updateable subscribers, immediate updating and queued
updating. Immediate uses a two phase commit process to carry DML originating
on the subscriber to the publisher, and queued uses a queue process to move
them to the publisher. Immediate requires always connected subscribers,
queued does not.

With updateable subscribers the majority of the DML should occur on the
publisher - its not really scalable beyond 10 or so subscribers. Merge is
tuned for large numbers of subscribers and has rich conflict resolution and
detection components which allow you to roll back conflicts. With updateable
subscribers the conflicts are merely logged and your conflict resolutions
are subscriber conflict rolled back, publisher conflict rolled back,
publisher conflict rolled back and a new snapshot sent.

To add to the previous comments, if you want to have offline access
(autonomy) then the choice is between queued updating subscribers (QUS) and
merge replication. QUS will be generally more efficient, but won't work for
BLOB datatypes and have a more restricted set of conflict resolvers than
merge.
    Cheers,
         Paul Ibison SQL Server MVP, www.replicationanswers.com .