"OTOH" is the slang acronym used primarily online for "On the Other Hand." It is used when a person wants to list items on both sides of an argument.
"OTOH" is often spelled all uppercase, but can be also spelled "otoh". All versions mean the same thing. Just be careful not to type entire sentences in uppercase, as that is considered rude shouting.
Example of OTOH Usage in a Discussion Forum
(first user:) I think you should buy that new i7 computer. Your current machine sucks.
(second user:) My wife would kill me if I spent 2 grand on a new computer.
(second user, again:) OTOH, she might like a faster machine in the house, if I can get her that interior design software to go with it.
Example of OTOH Usage in an Online Chat
(Kristin) Craig and I are thinking about getting a third dog. Our oldest dog Bailey is really old, and it will be really hard on Kobin when she dies and he is left without a dog companion.
(Sharmeen) Hmmm. That kind of makes sense. But is your yard big enough for three dogs?
(Kristin) Yeah, that's the thing, we'd probably want to get a small dog because the backyard isn't that large.
(Sharmeen) OTOH, you could get a cat instead. Cats are much more self-sufficient and lower maintenance. If Kobin and Bailey will accept a kitten into the house, that might be the way to go.
(Kristin) Never thought about that. That might work!
Example of OTOH Usage in Text Messaging
(Gurdeep) yo, are we still on for drinks tonight?
(Dustin) for sure. where do u want to meet?
(Gurdeep) Dilly says to meet him at Hudson's pub at 8 pm. the lineup gets busy there by 9.
(Dustin) parking sucks at Hudson's. OTOH, they make the best martinis there.
(Gurdeep) how about I pick you up at 7:40pm and we'll go in one car. That will make parking easier.
(Dustin) even better, let's take Uber so we don't have to worry about driving after we drink
(Gurdeep) good call. I'll get us an Uber ride and pick you up at 7:40pm.
The OTOH expression, like many cultural curiosities of the internet, is a part of modern English communication.
How to Capitalize and Punctuate Web and Texting Abbreviations
Capitalization is a non-concern when using text message abbreviations and chat jargon. You are welcome to use all uppercase (e.g. ROFL) or all lowercase (e.g. rofl), and the meaning is identical. Avoid typing entire sentences in uppercase, though, as that means shouting in online speak.
Proper punctuation is similarly a non-concern with most text message abbreviations. For example, the abbreviation for 'Too Long, Didn't Read' can be abbreviated as TL,DR or as TLDR. Both are an acceptable format, with or without punctuation.
Never use periods (dots) between your jargon letters. It would defeat the purpose of speeding up thumb typing. For example, ROFL would never be spelled R.O.F.L., and TTYL would never be spelled T.T.Y.L.
Recommended Etiquette for Using Web and Texting Jargon
Knowing when to use jargon in your messaging is about knowing who your audience is, knowing if the context is informal or professional, and then using good judgment. If you know the people well, and it is a personal and informal communication, then absolutely use abbreviation jargon. On the flip side, if you are just starting a friendship or professional relationship with the other person, then it is a good idea to avoid abbreviations until you have developed a relationship rapport.
If the messaging is in a professional context with someone at work, or with a customer or vendor outside your company, then avoid abbreviations altogether. Using full word spellings shows professionalism and courtesy. It is much easier to err on the side of being too professional and then relax your communications over time than doing the inverse.