I always dive with 2 computers. If I've spent a lot of money to be somewhere diving for multiple days, I want to be sure that if my main computer dies, my backup computer has my correct and current inert gas tissue loading so that I can continue diving with no impact.
But, that does not mean I think you need to buy 2 computers right off the bat. What I would recommend is having 2 computers as your long-term plan and buying your first computer based on that plan.
I am a tech diver. I am also a diver that only uses AI - even for my tech dives. My opinion is that if you get an AI computer, the only reason to buy an SPG is to have it in your reg bag, so that you can put it on your reg set if your AI transmitter dies and you want to keep diving. I have an SPG - several, actually. I take one along on trips but I have not used any of them since I initially removed them from my 1st stages.
If you're going to buy into hoseless AI. I would strongly suggest the PPS transmitter and a computer that will work with it. The PPS transmitter is the one sold by Shearwater, Oceanic, Aqualung, and others. Whatever the brand, they are all the same and made by Pelagic Pressure Systems. Any of them will work with any of the other brands of computers (that sell that same transmitter - i.e. PPS transmitters do NOT work with ScubaPro or Suunto computers, just for example).
If you're only aiming for normal recreational sport diving, any of the computers that work with that transmitter will do a fine job. I still have my very first computer - an Oceanic Atom 3.0. It has a plain LCD screen with a button to turn on a back light. For diving in clear-ish water, it is way more than readable enough. For night dives in clear-ish water, it is also perfectly fine. When it is not fine is when I'm diving in water with poor viz. But, from what I have seen, most divers that are only interested in warm water, good viz diving are not going to be diving in conditions where the basic backlit LCD-style display is a problem.
If you do anticipate diving in water that is lower viz, or if you think you might ever aim for tech diving, then I think the best computer on the market is the Shearwater Teric. If you can afford it, I can't imagine ever regretting spending that money. I have one (and a Shearwater Perdix AI and a Shearwater Predator EXT, and have had a Shearwater Petrel 2). I have a second Teric on order so that I can always dive with 2. That's how much I like it.
If your budget is not up to a Teric right now, then a less expensive computer (e.g. the Oceanic Atom or something comparable, since the Atom is now discontinued) that uses the same transmitter as the Teric would be a perfectly fine choice (presuming you're aiming to eventually dive with 2 computers). Get that basic AI-capable LCD computer and the transmitter now, then get a Teric (or whatever) later, which will share the same transmitter, and you're good to go.
What I would NOT do is buy a computer that you would not be perfectly happy diving as your primary. I.e. you go on a week long dive trip and your main computer dies on the first day. Will you be happy diving your "backup" as your one and only computer for the rest of the week? Whatever you buy now could be that computer, so choose wisely. That is why, just as one example, I personally would not buy an Oceanic BUD as a backup. I would not really be happy diving a BUD as my only computer for a week if my "primary" computer died on Day 1.
