Magento 2 : Bestseller and most viewed product on homepage

For bestseller create a block in __construct get instance of

\Magento\Sales\Model\ResourceModel\Report\Bestsellers\CollectionFactory $collectionFactory,

ex

<?php
namespace Sugarcode\Test\Block;

class Test extends \Magento\Framework\View\Element\Template
{
    protected $_coreRegistry = null;
    protected $_collectionFactory;

    public function __construct(
        \Magento\Backend\Block\Template\Context $context,
        \Magento\Framework\Registry $registry,
       \Magento\Sales\Model\ResourceModel\Report\Bestsellers\CollectionFactory $collectionFactory,
        array $data = []
    ) {
        $this->_collectionFactory = $collectionFactory;
        $this->_coreRegistry = $registry;
        parent::__construct($context, $data);
    }



    public function _prepareLayout()
    {
        return parent::_prepareLayout();
    }
    public function getBestSellerData()
    {
        $collection = $this->_collectionFactory->create()->setModel(
            'Magento\Catalog\Model\Product'
        );

        return $collection;
    }       

}

For recently viewed you can use widget from admin side or else you can write custom block with \Magento\Reports\Model\ResourceModel\Product\CollectionFactory $productsFactory

Look at:

vendor\magento\module-backend\Block\Dashboard\Tab\Products\Viewed.php

and

vendor\magento\module-backend\Block\Dashboard\Tab\Products\Ordered.php