As for think carefully before having DC's with a man who already supports his DC's from a previous relationship I would pick a man who pays for his DC's, rather than a deadbeat who doesn't, as the better father of my own child. Why wouldn't you?
eh? where's that strawman run off to? 
of course the one who pays is a better bet than the one who doesn't - who said otherwise? but the fact remains you are choosing someone who has prior financial commitments that will (or should) place restrictions on whether you can afford children or the size of the family you can have.
as to the personal question i'm asked here i personally wouldn't choose either man. i don't want to be with a man who is divorced and living separately from his children and i wouldn't want my son to be in that kind of family unit either. i wouldn't want to have children with a man who had already had children and wasn't a full, proper parent to them.
maybe controversial but that's my personal choice and feelings. i find men who live separately to their children and have an 'ex' who has the children to be unappealing and to have particular attitudes and behaviours i find unattractive and problematic.
i might consider a relationship with a man who has 50% genuine shared parenting with the mother of his children as i could respect that and see it as being a 'real' parent and not coming with the attendant attitudes of a weekend dad. i'd also be able to respect that he and his ex had managed to fairly and harmoniously deal with splitting up and being adult parents. such men are shrinkingly rare though.
i tend to be with people (friends, partners whatever) who i have shared values and ethics with. i don't find myself to have those with men who hate their ex's, make out she's a psycho bitch yet they chose to have children with her
and leave those children in her care. too alien for me.