If you have not been able to flip any of the dot nets but have had success in flipping the dot coms, I would stick with the dot coms.
I search probably up to 10,000+ dot coms every day and if I am lucky find one or possibly two that have potential commercial appeal to small / medium size end user businesses. I dont find it too difficult to sell some of them (I am not superhuman so inevitably they do not all find endusers) if I am careful about choosing them in the first place and keep the prices reasonable - not so sure how this would work with dot nets.
I am about 1 month into selling full time to endusers.
This month I have had the following sales:
M i c o r dot net - $975
T e k t i t e dot net - $300
MardisGrasBead(s)Shop.com - $150
1 three word .net for $185
SilverlineConstruction dot com $75
1 LLLL.com for mid $X,XXX
And I have two pending .com for mid $XXX
So, all in all not too bad for my first month. I also have about 30-40 domains which I havent even started contacting endusers for. I seem to be doing equally well with .com and .net. Alot of people say stay away from .net but I personally love them, I have found a few, some even with hyphens, that have already paid their reg fee in a month. They are a little harder to sell so I stick to generic two words or one word, just be prepared to slash your price.