this sounds a lot like the old netscape versus internet explorer battle. you could pick a browsing suite that did everything. or get a stand alone browser that was lean and faster. firefox gave us the best of both worlds with their plug-ins. you could start lean. and then junk things up the way you wanted based on how *you* used it. but the real difference is the rendering engines anyway. vivaldi is yet another blink browser without presto. and microsoft's spartan is starting to look interesting now that they've gotten away from their old way of doing things. they also built a supposedly decent new engine to replace trident. and you know their integration with windows will be second to none.
i tried vivaldi for a few days since part of my job is vetting desktop software for the company i work for. i think it's ok as far as it goes. better than a bulked-up firefox if you don't need the plug-ins. but i think vivaldi is too much old-think in trying to do everything. and the vivaldi developers make a lot of assumptions about how people want to do things. opera did that too. so like opera, vivaldi may be a winner. but mostly for people who match the user profile the developers are coding for.
i think it's worth trying to see if its for you. i'm going to stick with firefox for now. :-)