The size of a laptop is definitely one of the first things you'll need to look at when buying a laptop. There are a number of different sizes of laptops that are available on the market ranging from 10.5" to 17". Laptops can range from the bulky MSI GL72M to the thin LG Gram. The size of the laptop obviously affects its portability and also dictates the size of the keyboard and the touchpad.
Thinner laptops are usually lighter and easier to carry (not to mention the fact that they look really nice) one of the prime examples being the MacBook Air. But the downside is that they generally have lesser ports and are equipped with a smaller battery, which can be a deal breaker if you are planning on connecting a number of devices to the laptop. Thinner laptops are also usually more expensive as well.
3. Display size
As mentioned earlier, the size of the display will affect a laptop's portability. However, a larger display does mean a better experience when watching movies or playing games. So, ideally, you'll need to strike a balance between the size of the display you are looking for and how much you are willing to lift. You'll also have to take into consideration the size of your backpack. Some, like the Dell inspiron 15 7000, manage to cram a bigger display into a smaller form factor.
4. Display resolution
Another thing to keep in mind is the resolution of the display. Most laptops in the market either have a resolution of 1366 x 768 pixels, or 1920 x 1080 pixels. Higher resolution displays offer more detail, which makes watching movies or playing games fun, but reduce overall battery life, which is a pretty big drawback if you plan on using the laptop outdoors a lot. If you are buying a smaller laptop, a resolution of 1366 x 768 pixels should suffice. Some laptops, like the ASUS ZenBook Flip UX360CA offers an even higher resolution.
5. Display panel type
The type of panel used on the laptop should also be taken into account. Most laptops will either offer In-Plane Switching (IPS), or Twisted Nematic (TN) panels. Both with their own pros and cons. TN panels offer shorter response times as compared to IPS, making them ideal for gaming. They are also brighter, and more power efficient. The downside being a noticeable colour shift when viewing from angles. PS panels offer better viewing angles and colour reproduction. However, contrast may not be as good. Laptops like the Acer Aspire E15 E5-575 offer a TN panel.
Many people underestimate the importance of the keyboard. A good keyboard is especially important if you plan on typing a lot. Look for a keyboard with well-spaced keys, as a cramped keyboard makes typing difficult. Larger laptops usually offer more space, therefore, better keyboard spacing. The keys should be springy in order to make typing comfortable. Also, there shouldn't be flex in the keyboard itself. The keyboard should stay firm, regardless of the keys you press. Lenovo's ThinkPad series of laptops are known for offering good keyboards.
As for the touchpad, it is imperative that it is responsive to your touches. A poorly implemented touchpad will result in your pointer hopping all over the screen, or taps/double taps don't respond very well. A good touchpad is especially important when you consider that multi-touch gestures such as two-finger scrolling have become quite common. The touchpad area should also be pretty big and the left and right buttons should be responsive, but not spongy. The Apple MacBook Air and Lenovo's Carbon series offer good touchpads.
A powerful laptop will last you years and will be able to do practically any task you throw at it. The downside being that these are more expensive. Ideally, you choose according to what you plan on doing with the laptop. If you are looking for a device for word processing, with basic surfing and multimedia, a lower spec-ed laptop should do just fine. However, if you plan on doing a lot of video editing or similar work, you will need something powerful with a dedicated graphics card. Gaming laptops like the HP Omen AX248TX rule the roost in this regard.
Ports are also something you need to keep in mind. USB 3.0 ports are the newest types of ports and offer higher data transfer speeds as compared to older USB 2.0 ports. The newer ports are easily identifiable thanks to the blue colour coding. Ports that support the Thunderbolt 3 standard is also something you should look out for. Other ports your need to look at are HDMI slots that let you hook your laptop up to a TV or something similar. Laptops like the Asus FX553 offer multiple ports.
The bigger, powerful and feature-rich laptops are generally a lot more expensive as compared to the simple ones. So, there is a balance that you need to find between price and features. For example, the Acer Aspire ES1-572 can offer a basic laptop experience for just over 20K, but at the cost of some features. Its always best to try out the different types of laptops within your budget, before finalizing your choice.