Thai savings accounts will earn you very little: with the Primary Rate (the 'base rate') cut to 1.5% today - and likely to see 1.25% before year-end, banks cannot offer savings rates higher than this, without losing money.
The Thai stock market has performed poorly over the last couple of years (look at the SET Index) and, with the prevailing economic headwinds, does not look set to improve in the forseeable, so quity funds/mutuals don't look attractive to me.
Thai property on the other hand, remains quite attractive: a villa in Krabi/Phuket etc will yield 10-15% p.a. through rent alone (excl capital uplift): yes, if you're a foreigner (and unless it's a condo) you'll never own that property outright - but many developers now offer 30y+30y leases, to make the investment more attractive to foreigners.
Finally, look at international brokers that offer the ability to invest in overseas stock markets: the S&P 500 for example, is up c.10% YTD.
..Just my 2c.