Unless you are exclusively monf traited choose book. There are far more useful book legacies than there are staff. Creating a staff would boost dps but doubtful it would be enough to justify bring a monf lm in a dps role to a raid. The only good support legacy on staff is share the power, all the other legacies only boost spell damage. The book has both dps and support oriented legacies that are worthwhile.
how do you play your LM mostly? Do you do a lot of raiding and sit in AM most of the time? maybe a book may be more useful to you. Do you solo most of the time and just trait all reds? probably the increased dps from a staff would better suit you.
Do you find one of your current LI's just does not have enough LI points to set it up how you would like to? maybe pick that one so you can max out more legs
Do you have an LI that you are just not totally satisfied with and a replacement may work out better?
Your Tactical Healing Rating doesn´t matter as your healing output is very little compared to RKs and Minstrels anyway
While your book gets +% tactical damage, that is not only random between 1 and 6%, I think, but also less than the damage increase from a 1st Age Staff
Additionally a Book needs 5 majors while a Staff is fine with 3 or 4
I´d go for a Lvl 75 1st age staff and a Lvl 65 1st age book with at least +3/4% tactical damage and 5 majors
The Lvl 65 1st ages are really easy to get anyway
As others mentioned, it all depends on whats your playstyle is....
If you raid a LOT, main heal smaller groups, do content which requires AM traiting, then the 1st age book will be the preferable choice....because the advantages of the 1st age book are, better tact healing rating, better legacy values....mostly useful for AM traited play.....otherwise, the 1st age staff would be much more beneficial.....
The main choice is between having better tact healing rating or tactical damage rating.....the +x percent tactical damage figures that the book can identify with can easily be compensated by the big damage increase the 1st age staff offers.....
Personally I'd go for a staff....the second age book works very well for most content that needs AM traiting....even ToO.....I've had absolutely no problems raiding ToO with a 2nd age book....the difference in 1st age book and 2nd age book imo is not as significant as that between 1st age staff and 2nd age staff....
Pretty easy choice imo. 1st age book is literally no better than a 2nd age, unless you get the +5% tact damage. By why take the chance?
From lootboxes I've gotten three 1a symbols. I have both a staff and a book, and the book is worth getting. It's not as much of an upgrade from a 2a than a staff is but it's still worth getting. I'm happy with the base stats of +3% tact damage, -9% lore power cost, and +38.8 tactical heal rating. I'd say get the staff first, but the book isn't out of the picture if you get another symbol.
Hah, my lootboxes have contained class inappropriate gear and dresses:-) I'd almost always go weapon before book because the upgrade is so much less with a book unless it reveals a decent number of majoprs. I still have, and smetimes use, an L59 2A book in damage mode because it has a full set of majors (yes, its _that_ old!) Having pretty much all the bonuses does make the fire stack somewhat...
If a 1A took the max debuff levels usefully above a 2A then it would be a no brainer.