Most of them would presumably fight like cats and dogs on most issues. But their opposition is actually interestingly complementary, with possibly ruinous eventual consequences in my view. As for actual similarities, I think these may be clearer in the subcultural formations of their fandoms and in the media narratives they attract than in the candidates themselves. This becomes quite pronounced in the mansplaining and whitesplaining both fandoms are prone to, to put the point gently.
Bernie Sanders is a life-long fighter against racism and sexism -- occasional generational awkwardnesses in his communication of these commitments notwithstanding -- but there is a decided white male skew in his support that benefits him in the first two primaries, especially New Hampshire. This is doubly conspicuous given that Hillary's support is both less white and less male and so is the Democratic Party as a whole.
These issues are being displaced onto media narratives about a shared anti-establishmentarianism in both Trump and Sanders (although Trump populism is white supremacist and Sanders populism is anti-plutocratic so such analyses risk many distortions) and also a fairly phony competition between Clinton and Sanders over who is the most progressive candidate. Given their actual voting records both candidates are comparably progressive. Given his avowed democratic socialism (which I share) Sanders has the more progressive ideals -- but when the question is the pragmatics of arrival through legislation of more progressive outcomes this becomes a much more complex question. I for one think Clinton would be the more effective progressive President following the Obama administration -- but I will admit my view on this score does not seem to be shared by a majority of those who are as far left as I am, at least not yet.
I must say that I was quite enthusiastic about Sanders getting in the race and educating mainstream Americans on the substance of democratic socialist positions, which are not only correct in my view but more congenial to American values than is understood and hence would benefit from sustained public scrutiny -- but I have been profoundly disappointed that his candidacy has turned out to be more of an occasion than I anticipated for smug white male steamrolling of discourse and celebrations of symbolic over pragmatic politics in the Sanders fandom.
Look, I'll say it. I don't think Sanders is electable given my read of American culture which seems to me likely to disdain his curmudgeonly temperament (which I personally like and share) as unpresidential and to fall far war-terror fear-mongering which will declare him a dove with no grasp of the details. This scares me. The stakes are stupendously high. The GOP plutocratic Establishment/brainless bigot Base coalition verges on utter breakdown should the party fail to win the White House yet again (and this time after giving in to the Base's demands for once). Of course, Trump and Cruz and Rubio are even more loose-talking than Sanders on foreign policy, but Americans don't seem to mind loose talk when it takes on the belligerent tonalities of the right. Clinton's command of the details of foreign policy will reassure Americans if that is where this election is taking us, but her practice will be less bellicose (but still far from my cup of tea) than any of the Republicans likely to beat Sanders on this score. I find this prospect personally terrifying -- almost as bad as realizing what reactionary appointments to the courts would do to this country for the rest of my natural lifetime.
On domestic politics should the election turn on the economy instead, her enormously detailed policy papers on everything from financial reform to immigration, including their elicitatons of diverse stakeholder coalitions and strategic anticipations of likely objections, all strongly suggest better outcomes than the congenial chestnuts I am hearing from the Sanders campaign. Of course we can strengthen Social Security by raising the cap taxable income, of course single-payer is both fairer and more efficient than our for-profit system -- the policy wonks Clinton has on the payroll know this quite as well as the ones who have Sanders' ear. It's just that if making that abstract case got us from where we are to where we should be -- we would have already been there for half a century.
Needless to say, on policy the differences between Trump and Sanders are wider than the Grand Canyon. You better believe I'll vote for Sanders without hesitation if he becomes the nominee -- but I'll be scared to death about his chances to win and pretty resigned about his capacity to have coat-tails to summon a Congress to support his agenda. No doubt after the votes come in and Congress comes into session we'll find out what exactly "the revolution" he says we need practically consists of.