I have been using dongles for ages and three seemed the best. Asluck would have it I stumbled across T mobile doing their mifi for £10 pm instead of £15, for 10gb so took out a contract with them. One real advantage is now my phone, laptop and kindle all sync via this, where with a dongle this would not happen easily. I also have a gig on my orange phone, and as you surmise, one is better than the other, remembering t mobile and orange are the same. for convenience,definitely mifi, tmobile use the same one as three. For reception, perhaps consider a mifi contract and pay as you go with another provider. This works well with me, and is useful when the contract gigs are used up. One other tip, if in Ireland, get a PAYG 3 Dongle, you can use your allowance in the UK. Best if you phone them to register a card so you can pay on line as their site only accepts irish addresses. Once set up it is no hassle. Happy roving.
OnePlus 5 review