Are you an MSP asking this question who will be providing the product(s) to various clients of your own?  Or are you an end user who will likely buy one or two devices?

Support for end users typically is awful.  Support for resellers can be hit or miss.  I've heard horror stories and stories that made my jaw drop (because they were amazingly good).  

I'm not going to go into tremendous detail now because the answers really depend, IMO, on what your small business is (my first question).

Understood...I am the MSP who will be providing/supporting the products. Regarding my business, I provide IT solutions for virtually all facets of a business (digital marketing, web hosting/design, UCaaS, managed IT services, infosec services, and VoIP, among other service).

I'm looking to bolster my security offerings by partnering with a vendor in which I can leverage a next-Gen, proactive stack.

Thanks in advance for your reply.

Great response, and thank you! Insight is my distributor, and they have been extremely helpful up to this point. Again, thank you both for your responses, you have provided the info that i needed at this time.  

To be honest, as much as I love Experts Exchange (I've been a member here nearly since their inception 25 years ago), I don't think questions like this are best asked here.  

In the NYC/Long Island area, I run two user groups and subscribe to mailing lists for several other groups.  

Of the groups I'm a member of two are IT Consultants and MSPs only, one with dozens and one with hundreds of members.  The others are mixes of Consultants/MSPs and SysAdmins/Technicians. Everyone has their own opinion influenced by sales reps and personal experiences.  I would strongly recommend joining any or all of these groups (They are all closed but easily joined with an email to the list admins introducing yourself) and ask the question there.   (I'm not going to list the NY area groups as you're not in that area).

(Warning: some are popular, others are not so popular... messages can range from a few a week to dozens a day):
System Administrators: https://groups.google.com/g/ntsysadmin
Patching: https://groups.google.com/g/patchmanagement - parent website: http://patchmanagement.org/
IT Consultants (Founded for Microsoft Small Business Server 20 or so years ago): https://groups.io/g/sbs2k/topics
MSP focused: https://modernmsp.groups.io/g/msp/topics

To more directly answer your question (with the understanding that I'm but one opinion and the lists above can potentially offer dozens of opinions, including good contacts):
Palo Alto - Not a company I find is recognized in the SMB space.  Enterprise IT, yes, but SMB, not so much.
Cisco - Recognized for excellence (despite occasional issues), but expensive and as such, most MSPs/Consultants I'm acquainted with don't use.
Fortinet - I know several who use them  They've generally got an excellent reputation.  I looked into them a decade ago or so, but at the time, they had some limitations in how they worked that I didn't like (though I can't recall what they were).
Sophos - I have a friend and former colleague who tried using them in his SMB - NIGHTMARE to get support and some idiocy in the design when it came to redundancy.  
SonicWall - Tried them myself once a decade ago or so.  NOT impressed.  In particular, I bought a client a device that had issues out of the box.  But despite it being a new device, they wouldn't provide one bit of support without a support contract.  Bought the contract and support found it was bad firmware shipped on the device which I couldn't update without a support contract, so it was a brick unless I paid extra.  Demanded my money back on the support contract (they obliged), and never bought another SonicWall device.

What do I use and recommend?  Untangle.  www.untangle.com - small-ish company with very good support, offers both a free and a paid product, can run as a VM, on your own hardware, or you can buy one of their devices.  Easily configured with many features.  Reasonable price and direct partner relationship.

Oh, and as for distributors - I use D&H.  I've found them very helpful on a variety of issues and excellent shipping and back order policies.  The D&H search also works well.

I tried Ingram years ago and was frustrated with them as most things were cheaper if I bought off Amazon, NewEgg, or Micro Center.  (Frankly, that still happens with D&H, but I can sell Microsoft licenses and complete systems for cheaper than I could get elsewhere).

I also have an Account with TechData (which I think merged with Synnex).  TechData's search is AWFUL.  I've given up on ordering most things from them it's so bad.  Their pricing is GENERALLY slightly better than D&H, but given it'll take me 20mins+a phone call to find what I'm looking for at TechData vs. 3 minutes to complete the order at D&H, it's overall cheaper at D&H when you value your time.

Great info! Both of you have mentioned Synnex, so I will look into them. Please excuse the ignorance, who is D&H?

Point taken regarding the feedback on the security vendors, and once again, great info. I'll definitely look into the groups you mentioned as well. I'm not familiar with untangle, but will be doing research on them as well. I would like to add that i've deployed a few of Fortinet's NGFWs and they are surprisingly very tech friendly regarding the user interface, config, security features, etc,; i was just unsure regarding engaging them as a potential partner, but i take your advice all the same.

D&H - https://dandh.com/v4/view?pageReq=dhMainNS
Another bonus for me - D&H accepts American Express; TechData/Synnex does not.