Katana is fairly light on endurance.
SR and Regen both benefit from Divine Avalanche, Regen benefits more since it lacks defence to begin with.
You can get to the soft defence "cap" in PvE (for lethal/melee damage) using only Divine Avalanche... obviously if you can attain this and still have a lot of heals from your secondary (Regen) you will be better off than if you overshoot the cap and "waste" +Defence (SR). The flipside is that SR only has to use DA half as often as Regen (one DA buff up all the time) to hit the cap, where Regen has to have it double-stacked to hit the cap... this means when a SR is at the cap they will have slightly more time to use more damaging attacks.
Slotted Normally? Dull Pain is 180Secs Recharge, 120 Secs Duration. You can get it perma with +recharge from IOs and Hasten. Reconstruction is up every 30 Secs. IH is up a bit over every 5 minutes, and lasts for 90 Secs.
With Hasten, Dull Pain downtime is between 18-30 seconds, depending on whether it gets Hasten during the downtime or not.
Without Hasten, Dull Pain is about 60 seconds
Reconstruction is available every 30 seconds without Hasten, every 22 with it.
Instant Healing has a downtime of about 3 minutes with Hasten, 4 minutes without.
This assumes all are slotted with 3 Recharge SOs ( or equivalent ).
Regens are slightly less good for large teams ( need to be more careful of AoEs ) but SR are slightly less self sufficient because of a lack of self heal ( mainly a problem in small teams with no support toons ). Solo neither have a problem, as SR can heal using inspiration drops and scrappers really only need their primary and mez protection to solo anyway.
The main advantage for Regen is the build is going to be far less tight ( not needing stamina ASAP and SR pretty much needs the whole secondary set ), although I think Regen may need more slots early on.
@Unthing ... Mostly on Union.
As other ppl said in similar threads, regen makes things easy and sr makes things fun. Katana works well with all secondaries.
I got upto lvl 40 w/out p'lvl in about 3wks. and im a Kat/Regen Scrapper ... I can solo just as well as i can play in a team. I have no AoEs i took them all out as Aggro will kill a regen scrapper
Regen Scrappers and a Kill or Be killed build. So be sensible if u do it.
Kat/SR is heavy on End so Stamina will have to be taken asap. But once u get Elude (lvl 38) u can Cope with the aggro gained from your AoE attacks. granted u still gotta be careful but SR are for the more adventurous whilst regen are for the more kamikazi style player (kill or be killed)
Depends what u like ... both will need Inspir's fairly often but regen wont hardly ever need blues.
I'll leave it to u what to decide 
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where Regen has to have it double-stacked to hit the cap... this means when a SR is at the cap they will have slightly more time to use more damaging attacks.
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True, but with IO sets and careful slotting, DA can be both excellent defence and a reasonable attack.
During the last weeks i have tested several scrapper builds with both different primaries and secondaries.
I have now decided to build a Katana scrapper with either Regen or SR. I've played both power sets on chars until the end-twenties and havent seen major differences in survivability in PvE.
So, how does these sets work in combination with Katana for PvE?
Is the increased defense from DA with FF overall better then the heals from regen if fighting for a longer time ?
What is the downtime of Dull Pain, Reconstruction and IH,
if i have to use all heals in short time?
Is Katana more end using so it might be better to take it with Regen than with SR?
Thx for any advices.