Asus has launched a rather nice range of smartphones, called ZenFones. There are three ZenFones to choose from, each with a different screen size, slightly different the specs and an adjusted price tag that reflects those various differences. See also: Best smartphones of 2014.

If you're looking for a budget smartphone, the ZenFone 4 is just £99, while the ZenFone 5 comes in at a mid-range price of £180 and the ZenFone 6 sits in the phablet category and is priced at £250.

The most obvious difference between these smartphones, aside from the price, is the screen size. As you may have guessed, the ZenFone 4 has a 4in display, the 5 has a 5in display and the 6 has a huge 6in display.

They each have similar designs, with the same ceramic coated plastic back cases. They can be removed and switched out for various new colours. Beneath the back cases you'll find the MicroSD slot, which allows up to an additional 64GB in each smartphone, and the SIM-card slot (or two on the ZenFone 6).

We like the small portion of metal along the bottom of each ZenFone, and the metal buttons, which all feature Asus's trademark concentric circle design, helping to make each smartphone look more premium. The biggest downfall, though, is the lack of a backlight behind those buttons at the bottom of each display.

Read: Motorola Moto G 2014 review.

The displays on both the ZenFone 5 and ZenFone 6 are HD 1280x720 IPS, which means the ZenFone 5's smaller display has a higher pixel density. The viewing angles are amazing on both smartphones and they're bright and crisp.

The ZenFone 4's display is much less impressive, without those amazing viewing angles made possible thanks to the IPS display and with a much lower resolution of 480 x 800.

All of the ZenFones have the Splendid app installed so you can adjust the colours to suit you.

All three ZenFones have an Intel Atom processor, though they're clocked at different speeds. That's paired with 2GB RAM for both the ZenFone 5 and ZenFone 6, but the ZenFone 4 has just 1GB RAM. We found all three smartphones to be reasonably speedy, and were pleasantly surprised by the performance of the ZenFone 4 considering its price tag.

Connectivity is the same across all three smartphones, with WiFi, though its not the faster 11ac standard and Bluetooth 4.0 but no NFC or IR blaster.

If you're looking for 4G, though, you'll need to buy the second, more expensive model of the ZenFone 5, which in addition to 4G also has a different processor.

On to cameras now. We love the camera on the ZenFone 6 but were disappointed to find that it wasn't used in the ZenFone 5 too. The ZenFone 6 has a brilliant 13Mp camera, but the ZenFone 5's 8Mp camera isn't as good, and the ZenFone 4's 5Mp snapper is quite terrible and doesn't come with a flash.

They're all capable of capturing 1080p video, but we found all of the videos we captured across all three devices to be laggy.

Asus's camera app is brilliant though, providing lots of features, filters and effects.

In fact, we like most of Asus's apps, which are part of its Zen UI interface fro Android 4.3 Jelly Bean. It's colourful, flat and minimalistic and very simple to navigate, and we found it a joy to use. Stock apps include What's Next and Do It Later, which help you stay on top of your schedule and to do lists.

Battery life of both the ZenFone 5 and ZenFone 6 is outstanding. We found that we could use both devices for two days between charging. The ZenFone 4 is less impressive but still good, lasting for a day between charging so you'll need to plug it in once a day.

Overall, we're pleasantly surprised by the Asus ZenFone range. There's a smartphone to suit everyone here, whatever your budget and whatever screen size you prefer. We're excited to see what Asus has up its sleeve next, and we expect rivals will be curious and perhaps slightly worried, too.