With the Christmas season now upon us and deals raining down on mobile handsets, you might also be in the market for a new SIM. Three's fully unlimited deal is still one of the best ones around. It's affordable, 5G compatible, and on offer.

At £20 per month, it's the cheapest unlimited SIM deal out there. The first six months are also discounted to £10 per monthHead to Three to check out its Unlimited data SIM deal.

The full term for the SIM is for 24 months, but if you don't want to commit for two years, there's also a deal on the 12-month unlimited plan. This plan costs £18 per month through the whole 12-month term, which is down from the usual £20 per month.

With nearly every network offering unlimited data SIMs, it may be hard to choose which one is best – but not all unlimited SIM offers are created equally.

Vodafone, for instance, has its own unlimited data options (that are also 5G compatible), available in three tiers: Unlimited Lite, Unlimited, and Unlimited Max. The primary difference between the options is the maximum download speed, which is important to note before signing the dotted lines.

The download speeds the network allows should match your browsing habits. You don't want to lock yourself into a long term commitment that's incompatible with streaming or social media, for example, if that's primarily how you spend your time online.

Vodafone's cheapest unlimited SIM, the Unlimited Lite, is more expensive than Three's, though it only offers a maximum download speed of 2Mbps. Three's speeds, however, may range from 21Mbps to 30Mbps, with no speed cap. Keep in mind, the maximum speed on Three will depend on your location, so be sure to check your area coverage first.

EE offers faster download speeds on average, its unlimited plans start at £34 per month for 4G coverage, while a 5G-compatible unlimited SIM costs £44 per month. See all EE SIM-Only deals.

O2's unlimited data plan are priced similarly at £35 per month for 4G coverage only, but also has one of the slowest download rates compared to . The carrier plans to offer 5G coverage in October.

Three's deal offers the best value in the market when considering speed, price and coverage. You can also use your phone has a hotspot. Check out Three's Unlimited data SIM deal now.

For more SIM only deals see our dedicated round up.