There's no one right answer. I think it depends on what you're trying to achieve, and I have not yet found a truly excellent, integrated solution to integrate all of the data. Most small/early stage companies I know simply to their best to put the data together in periodic, spreadsheet-based summaries.
I've been looking at Allyde as an open source solution, which of course means it's inexpensive (free) but might not have all the features you need. The good news is that you can add them if you want; the bad news is that you'd have to code. Fancier solutions (HubSpot, Marketo, etc.) are excellent but expensive.
So this brings me to a broader point: As I counsel my clients, current and past, it's also important to decide what you want to measure at each stage of your buyers' journey (i.e. funnel), and to realize that some investments don't have easily measurable ROI. At minimum, knowing a key milestone in the buyer's journey and focusing on that metric is key. For example, you may know that people who watch a webinar are more likely to buy than others, so focusing on webinar attendance as a key metric would be wise. Which vehicles - be they traditional banners/newsletters, social, content or whatever - seem to get you more webinar attendees? Focus on those. (That's just a random example: yours may be "downloaded a white paper," "Opted in," or whatever seems to influence conversions most.)
In my experience, spending the time to look at the overall buyers journey and then concentrating on one key metric works best. You can and should periodically revisit the more in-depth analysis, but for day-to-day and week-to-week, one metric helps you and your team focus your efforts and expenditures.