Smartphones have become a de facto mobile "PC" for many consumers. And that trend will only intensify as phones gain bigger screens and get more sophisticated.  Here’s the top picks for 2015.
iPhone 6s and iPhone 6S Plus: the 6S Plus is Apple’s second stab – following the 6 Plus -- at building a big phone. The stand-out hardware for the second-gen 5.5-inch iPhone is the camera, jumping to 12 megapixels from the 8 megapixels of the previous generation. The smaller 6S (4.7 inches) boasts pretty much the same camera specs but doesn’t have the optical image stabilization (which mitigates blur) of the 6S Plus. Both phones are capable of taking very-high-resolution 4K video.
High-quality cameras have become the sine qua non for top smartphones – and can be the difference between a successful product and an also-ran. Apple revealed recently that it has hired more than 800 engineers to work solely on the camera. (http://www.cbsnews.com/news/60-minutes-apple-tim-cook-charlie-rose/). That’s how important it is. And Apple continues to offer one of best smartphone cameras out there.
Other new additions with 6S and 6S Plus include a 3D Touch display that is sensitive to how much pressure is applied. For example, by pressing firmly on the left edge of the phone, you can call up multitasking and flip through your open applications. Or exert more touch pressure on an icon and you activate shortcuts.  It’s not a huge addition to the iPhone but it makes a great phone even better. 
One of the best things about the new iPhones is under the hood.  A new A9 processor makes it one of the fastest smartphones on the planet.
But new hardware aside, it’s all of the apps that make it hard to go wrong with the iPhone. The iPhone is the gold standard for mobile apps and just about any app worth its salt is available on the iPhone.
Samsung Galaxy S6 and Samsung Galaxy S6 Edge: While the S6 Edge isn’t fundamentally different than the less-expensive S6, its unique display makes it much more of a looker thanks to the curved display that waterfalls on both sides. Both the S6 and S6 Edge use OLED display technology (versus Apple’s slightly less eye-popping LCD). The screen’s 5.1-inch Quad HD (2,560x1,440) resolution is a bit of overkill – but then who’s counting pixels.
And we’re just getting started. Samsung, like Apple, takes camera technology very seriously and it’s a toss up whether Samsung or Apple gets the best camera crown. Samsung offers a 16-megapixel shooter that produces excellent results. 

Samsung’s Galaxy S6 and S6 Edge also fare well on performance, though the newer Apple phones perform better on some key benchmarks. 
A distinct iPhone-besting feature is the S6’s and S6 Edge’s fast charging, which gets you another four hours in about 10 minutes of charging. Other new notables include a pared down Android (read: less bloated) and a metal chassis design, which is a big step up from the plastic S5. The bottom line is the Galaxy S6 and Galaxy S6 Edge are the Android phones to beat.
Samsung Galaxy Note 5 and Galaxy S6 Edge+: Like the iPhone 6S and 6S Plus, Samsung has a big/bigger duo. Except the tally for Samsung is four separate phones (see Galaxy S6 and S6 Edge above) versus two for Apple. The flat-screen Galaxy Note 5 and dual-curved-edge S6 Edge+ offer a similar dynamic to the S6 and S6 Edge – except at a larger size, 5.7 inches. That said, there is one big difference: the Note 5 comes with Samsung’s S Pen stylus (thus the “Note” branding). And the Note has a curved back, which the Edge+ doesn’t have (the curved edges on the Edge+ intersect with a flat back). They both also offer good battery life.

Google Nexus 6P: Maybe the best Nexus phone yet. Huawei, the China-based manufacturer of the Nexus 6P, is on the rise and is now ranked as the No.3 global smartphone supplier behind Samsung and Apple, respectively, according to market researcher IDC’s most recent data. The 6P, a collaboration with Google, is Huawei’s first major product in the U.S and the first all-metal Nexus phone. It competes head on with the iPhone 6s Plus and Samsung Galaxy Note 5. Specs include a gorgeous AMOLED display, a Qualcomm octa-core (8 core) processor, 32GB of storage (base model), 3GB of RAM, and 12.3-megapixel (4K video) camera. The Nexus 6P has a good camera and a conveniently-positioned fingerprint reader on the back.
HTC One M9: HTC One M series phones are perennial favorites. The One M9 follows the well-received M8.  Like the M8, its metal design makes for one of the best-looking smartphones on the market. If you liked the M8 (which many reviewers did: http://www.cnet.com/products/htc-one-m8/), the M9 is similarly attractive. The problem is, the competition has changed. But it’s still a good phone (with a decent but not great camera) and HTC offers a no-questions-asked replacement policy in the first year of ownership.
Microsoft Lumia 950 XL: it would be remiss to leave Microsoft out of a top 10 list because they do make good phones. The challenge dogging Microsoft is that there are two practically-unassailable dominant platforms – Apple’s iOS and Android. So, Microsoft phones are invariably relegated to also-ran status due to their small market share and lack of apps. That said, the recently-released Lumia 950 XL has a great camera, beautiful 5.7-inch AMOLED display, a fast processor, and a buttery smooth interface, courtesy of Windows 10 Mobile.
Moto G 2015: a good inexpensive smartphone. The 2015 version has a new design, water resistance, and improved camera. It’s not the fastest smartphone you’ll ever use but if you opt for the model a step above the entry level version, it’s a good deal.