I grew up pure Lionel, definitely anti- HO.
since then, I met some wonderful HO operators who invited me to an operating session. With their help, I've seen and operated on several HO railroads. I am now an HO believer.
I now dabble in both HO and O 3 rail.
Cost: That's a no brainier. HO definitely is least costly.
As an example, I have an Atlas HO Gold series GP40 on pre-order, true scale dimension, DCC, realistic sound, $187
Compare that to my O gauge MTH GP40 pre-order from a MTH dealer is over $400.
99% of all my rolling stock (both HO & 3rail) is bought on the secondary market ( eBay and here on the forum), again, HO is a no brainer.
My HO CSX Coal Porters cost me about $10-$12 each(walthers Gold series)
Contrast that to my O gauge MTH CSX coal porters that are about $30-$40 each
Walthers Shinohara code 83 switches are about half ( or less) than comparable Lionel Fastrack or MTH switches. Walthers offers a lot more choices in variety of switches than either Lionel or MTH. Ross Switches helps to even the variety available. Bachmann EZ track (with roadbed) is the HO equivelant of Fastrack.
Buildings? Walthers HO Cornerstone Building kits offer an incredible variety.
Size? HO is fine if you keep the height of your table up around 42" or more.
Operation? I've seen issues in both HO and O gauge. Careful track work and proper wiring is required in both scales for trouble free operation.
Operating accessories: Clearly O gauge has the edge, no contest. Problem is that most O gauge accessories are not to scale.
Operation: HO has a small edge with their Kadee couplers. With delay effect, switching is easy to do. If you're just a loop to loop guy then couplers don't matter.
I could go on and on but in the end, I'd suggest doing a bit of both. That will satisfy that "should I" craving.
i suggest that you look into connecting with some HO modelers who can help you. Visit as many railroads as you can, ask questions.
In the meantime, enjoy!