It couldn't be more on topic   Welcome.

Bittrex and Cryptsy have the highest volume. There is some fishy stuff going on with Cryptsy & users have been reporting issues withdrawing bitcoin, but UNO withdrawals have been working perfectly for months. So if you decide to use Cryptsy I recommend using it only to buy UNO. Bittrex is safe for both buying and selling, I've been using it for over a year with no issues. Just use 2fa for extra security.

Bleutrade and Cryptopia are much lower volume, but they have alt-UNO pairings that can be arbitraged if you're patient and happy with a couple dollar profit per trade. Those are also good exchanges to place some optimistic orders (high asks and low bids, like 5-20% above or below market rate). They are both reliable exchanges from my experience over the last 6 months or so. Cryptopia is good for placing normal trades since it has the lowest trade fee, 0.2%, and often gets $100+ volume per day. 0.2% isn't much lower than the 0.25% on Bittrex and Bleutrade though so don't let that be a deciding factor. Keep in mind that Cryptsy has no trade fees but charges 0.5% to withdraw.

I use this page regularly to check the markets: http://coinmarketcap.com/currencies/unobtanium/#markets but you can also use the site that FallingKnife posted above, coinhills, it features some more of the smaller alt-UNO markets.

Also, don't forget about the block explorer https://chainz.cryptoid.info/uno/# there you can monitor exchange wallet sizes, node count, hashrate, daily transaction volume, etc.

Let us know if you have any other questions.