Chainlink, Band, Dia - some of the most known Oracle protocols which seems to be something like golden sheep for most of the crypto enthusiasts.
But, what it is about, where they are coming from and how is the future?
Let's start with a short introduction.
What is an Oracle and what role has it in the blockchain ecosystem?
TL;DR: A blockchain is a closed circuit. Everything is developing and changing inside it, so it could be controllable and secured. This is a good fact. The bad one is that we cannot have access to outside info, so we are stuck without the possibility of executing a Smart Contract that depends on some terms.
I'll give you an example:
I want to agree the selling of some Oil through a Smart Contract (this means the contract is executing by a software, independent of humans, when some conditions are reached) if the price for oil is growing to 50$. Well, at that price, my Oil is sold.
But, how can the Smart Contract know the oil prices (in secure conditions, I mean - the info should be true) ?
It cannot until interacting with an Oracle, which brings the data from the outside, verify it and after that is releasing it in the blockchain to be used.
That is what an Oracle is good for.
Oracle world
this is a list with all Oracles I found already listed:

Of course, some of them doesn't offer oracle services for others, but for them (like Augur, Idena, API3 or UMA, for example).
I will not comment about the most acclaimed Oracles: LINK or BAND, but will try to have a look to the ones with the smallest MarketCAp to see if there is something to monitor.
Going upwards:
Idena - coming from ID - is not an Oracle service like Chainlink. Is related to other things and is based on Proof-of-Person consensus.
Zoracles instead is looking quite good: actual MarketCap - 3,7 million - 10.000 tokens Max Supply (5035 is Circulating Supply). They claim to be a Zero Knowledge oracle. The liquidity is fair enough - around 400 k $, so, the perspectives looks nice. Take a look at it.

Oraichain Token is another possible gem because of their potential. They includes Artificial Intelligence for interacting with Smart Contracts and some partnerships onboarded with Rikkeisoft and Kardiachain. This is the reason they cancelled the private sale. The didn't need it anymore.
Oraichain is a data oracle platform that aggregates and connects
Artificial Intelligence APIs to smart contracts and regular applications.
The world’s first AI-powered data oracle has arrived.
They announced yesterday a predictible token burn program and they will have finally only 23 million tokens instead of 86 millionMax Supply. This 73% diminishing supply is interesting and is paving the way of a token price increase.
Even now the MarketCap is rather unimportant (5.3 million) vs DIA, for example or TRB, which are more than 30 million.
The only issue is the way of releasing the rest of the tokens, but they explain it here:

DOS Network is the next in place, with a 12 million MarketCap, but only 136 million Circulating Supply from a Max of 1 billion. If we compare it with LINK, there is more way to grow, but if we go to BAND, we are almost there if we purge all the tokens. Take care with this.

There are some good things about it:
DOS Network - A Decentralized Oracle Service supporting multiple heterogeneous blockchains. DOS Network brings real word data, event and computation power to smart contract in a secure, reliable, efficient and scalable way.
Also, they are listed, besides Uniswap, on Poloniex, Balancer, Gate.io and, soon, (I think, because I saw they are partners) - on Bitmax.
We are going now in the middle league, where we meet the first proposal:
Zap.org is building a Source Agnostic Oracle Network. They try to get the IOT (Internet of Things) market in this could be a good niche for them.
They had released half of their tokens already (240 million from 520 million) and the MarketCap is now 32 million. All they have to do now is to confirm their utility through as many partnerships they can.

A minus could be the places where is traded (Bitrue - by far, the most important market), but you can find them also on Uniswap.
Then Tellor (TRB) and DIA follows, these are known enough Oracles and I think it will have a nice future, so the actual price and MarketCap combined with the number of tokens and their Roadmap and partnerships will go to a nice profit. I'll bet on Tellor because of their very small token number and because almost all are already in the market.


API3 is not an Oracle, but a Decentralized API, so we go to
NEST Protocol is the first oracle network to produce price data on chain.
Maybe, I could not say anythings else at this moment, but despite of their already good MarketCap, I am a little circumspect regarding the trading markets where the volumes (and the price are made): IDCM, Coinbene, HBTC.

A new unlisted project is Razor Network
Is one of the newest projects which raised 3.7 million $ in a seed round from some investors, including Alameda Research, the owner of FTX exchange and Sushiswap.
Razor team has said it is attempting to distinguish itself with a dispute-resolution mechanism for protection against attacks, citing Chainlink's exploit that occurred in late August 2020
Expected to be launched in Q2 2021.
Conclusion
The Oracle market is bigger than I thought, so you can pick some to hold for 2-3 years. My choices are: Zoracles, Oraichain and Tellor, but it's only my personal bet.
Don't forget, always DYOR.
Cheers!