I'd recommend Dual Blades/Willpower.
If you want the flavor of the month secondary, but without all the investment, may I suggest sword and board (Broad Sword/Shield Defense)? I've had a blast with mine (currently 43), and it's been one of the most survivable scrappers I've played. On top of that, if you DO spend the influence, it'll tear through AVs just fine, just a little more slowly than DM/SD. I suspect it is particularly well suited to Architect Entertainment missions, where Parry should be able to send you enough over the soft cap to deal with all of the to hit buffs.
Broad Sword/Super Reflexes should also do well at Architect Entertainment, and for the same reason. I'd probably rather have the damage buff from Against All Odds than softcap to all positions on a budget, but it's really not a bad choice.
My Dual Blades/Willpower is my most recent 50, and I had a lot of fun playing him, but he's probably retired now.
A very common recommendation is Katana/Willpower. Very solid, no real weaknesses, strong at all levels, no endurance trouble, doesn't give up anything at the top end. The basic idea is that combining the defense from Katana with the regeneration in Willpower makes for a very potent combination. Also easy to get into and hard to mess up, since you just toggle up and go. Willpower very much just fades into the background and does its job. On the other hand, it might seem a little boring, particularly after playing Regen and Dark. Regen and Dark have personality. Not so much with Willpower.
"That's because Werner can't do maths." - BunnyAnomaly
"Four hours in, and I was no longer making mistakes, no longer detoggling. I was a machine." - Werner
Videos of Other Stupid Scrapper Tricks
My main reasons for choosing DM with SD are Dark Consumption and Siphon Life. I can't stand slowing down because of my endurance and the heal increases the survivability by a ton. Even without spending a few hundred million inf it's a great combo.
I'd like to know more about what you're looking for though. AV soloing without inspirations, soloing swarms of enemies, basic soloing, teaming, little bit of everything or something else? High damage or high defense? Good endurance management? Proactive, reactive or passive defense?
For leveling purposes, I'm guessing that hitting the melee soft cap early and easily is more valuable than the heal from Siphon Life. I can't argue with Dark Consumption, but I will say that I just haven't had serious endurance issues on mine. It was just a matter of taking Stamina and frankenslotting my attacks, nothing expensive.
I can only imagine the awesomeness of Against All Odds + Soul Drain + Shield Charge, though. 
"That's because Werner can't do maths." - BunnyAnomaly
"Four hours in, and I was no longer making mistakes, no longer detoggling. I was a machine." - Werner
Videos of Other Stupid Scrapper Tricks
That BS/SR sounds promising (of course I'm biased because my main is one). At that level you should be getting close to Stamina, and Parry will be a real help getting you by until you bloom in your thirties.
Yeah, BS after Stamina & SOs is like morning after a long, cold night. And stacked Parry just gives SR more of a good thing.
And then you get Headsplitter. 
Thought I'd roll a new scrapper to get to know the game again....
I'd like something that's tough enough that I won't get annoyed with it, so I'm looking for more powerful builds until I get to know the game again.
Skimming the boards, it sounds like /SD is the flavour of the month, which could also be fun just as a way to get to know one of the new powersets. I think I'll take that unless I hear otherwise....
Sounds like the primary of choice is DM/, but only if you've got the money to build it out to max efficiency, which I don't (probably got ~200M inf or so across my various alts). Should I consider Fire/ instead? Or something else?
Scrappers I've previously leveled are Spines/Regen and Spines/Dark, plus I have a level 20-something BS/SR that I suppose I could dust off. My objective would be for this new toon to become my main.
Thanks for the advice....