No matter what "wood" you use, you will have some distortion like warping or bowing or "something". Personally, I do not like to use wood for this sort of thing, especially if it is totally painted.
Actually MDF is a decent choice because it is more stable BUT it is rittled with "fuzzies". It also chips and breaks off small details with small cross sections. After a decent coat or 3 of a good primer the fuzzies can be sanded away - lots of labor of love.
The BEST material is HDU (brand name sign foam or equivalent) It is VERY easy to machine, takes details VERY well and paints VERY well. There will be NO fuzzies to sand off. HDU is impervious to weather. HDU when painted will not crack, peal, bubble or rust. I just got a sign back from a customer to be repainted a different color and looks like I just finished painting it. The sign is 4 years old. I pressure washed it and not even a speck of paint came off the sign. The down side is how to get it - and the cost, as it is very expensive. I set up a commercial account at a local sign shop and buy it from them. Sometimes the local sign shop has damaged sheets at discounted prices. I always look for that.
Other things are Corian, PVC (can get AZEK at Home Depot) and sheet insulation foam. All things have their up and downs, For TINY stuff Corian is the absolutely best.
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