Hands down, your site/ blog.  Then social share it and get the word out.  Not even a close comparison.

I have been testing this thoroughly for the last two years.  I am aware of that article, but it has a lot of the blind leading the blind in my opinion.

The first thing you have to decide is whether you are going to use both address lines or a single one.  Google tells you to use the second address line for your unit # or suite.  Everyone else tends to lean that way because Google does.  Unfortunately, this does not play out in the real world.  There are lots of sites that scrape and pull data, and many of them ignore Line 2.  If you doubt this, then test it and you will start to see all the sites that don't have your suite or unit.  So you get a lot of broken citations that don't have the # or suite on them.  I can't stand this inconsistency, therefore I have chosen to not use the second line - ever - and I think it has paid off.

So now to address your question.  You should choose either Ste or #.  The only caveat you might consider is if your client has had tons of citation work in the past with Suite spelled out, and even then it still might be worth it to clean it all up.

'Ste' is the USPS version and a lot of sites still scrub their data and convert it to USPS, so even if you use '#' it might get converted to USPS.  On the other hand, if you use 'Ste', InfoGroup (ExpressUpdate) will convert it to '#' no matter what, and every site that pulls its data from them will have the # in it.  So how do you decide?

We have tested it both ways.  Up until about 4-5 months ago, we found the 'Ste' method to be our preferred method.  Then we started noticing in Google+ Local that they started converting the 'Ste' to '#'.  [SCREAM]

So here is my recommendation (for what it's worth)...

On all new campaigns that haven't had anything done, use the Line 1 address only and use '#' instead of 'Ste'.  Also, we have found it best to have the # next to the number without a space - for example, use '#400' instead of '# 400'.

If you have an existing campaign running where you have used Ste or Suite, you will need to decide if there is any reason to change it at this point.  If all is going well, don't mess with it.  If you have not been getting your desired results, then consider changing to my recommendation above - just make sure you cover all of the major data aggregators, search portals, review sites, IYPs, and biz directories with your new change as quickly as you can.

I know this might be controversial (since it includes ignoring Google's recommendation about using line 2), but just sharing our opinions based on a lot experience testing this specific issue over the past couple years.

Another option is Twilio Open VBX, which is available from Twilio for free. Requires a little bit of effort to setup, but not too complex and takes about 20 minutes.  Once setup, create and link your Twilio account to it.  Then you can create a new number instantly any time you need one for this purpose ($1 a piece).  You create it, forward it to your phone for verification.  Use each number for up to 4-5 Google accounts.

If you dive into Google Analytics/ GWT, you can get some great information like this - and it's free.  Not sure the exact reason you want to follow specific individual behavior, but if you are trying to gather more intel on how "hot"  your prospect is, then you may want to consider looking into marketing automation software.  These are designed to track individuals and score them.  They can even integrate them into your CRM like Salesforce.

Do a search for marketing automation software.  Here are a few to consider, from low cost to higher cost, higher functionality:  Optify, Act-On, Hubspot, Marketo.

As long as you have your authorship set up properly on your primary blog, and you are linking to it, it likely won't hurt your primary blog/ site - unless you get carried away and post it on dozens or hundreds of 3rd party sites.  Make sure it gets indexed on your original site first, before publishing elsewhere.

I understand you may be wanting to keep the blog post in its entirety on the 3rd party sites in order to provide value, but I would recommend that you use really solid summaries/ excerpts and then "click here to read more" type link that takes them to the full article on your main blog.  They will still get the full value, and you will get the extra targeted traffic to your main blog.

Definitely stay away from listing all 3 across there like that.  Based on the search numbers you have provided, and assuming that they are equally competitive as you have stated, here is a suggested title:

Managed IT Services and Support | Company Name

You could replace the pipe '|' with 'by' if you wanted to make it flow better in the visitor's mind.

This focuses on your most searched term for this page (since they are equally competitive, go after the volume).  You will not be neglecting the other 2 by doing this, as the search engines are smart enough to understand the association as long as you have good copy on the page.  We have lots of pages that rank #1 without the keyword in the Title tag.