340 Vs 360 which is better?

The short, short version...
You can build either, for similar money. But, you can't buy a 340 for anywhere near what 360s can be found for.
As far as performance... For a street car, I'll take stroke length any day over any bonus others think a 340 has. Plus, you're only 16. You have yet to learn that many of the guys you see on the street that have air cleaners that say "427" or "350" or "340" are all running 396s, or 307s, or 318s. Visually, the 273, 318, 340, and 360 LAs are identical in appearance, unless you have a very seasoned eye for detail.