I don't post often, but read alot...Good question. I've tried many colors and finishes, looking for that holy grail, but come to find out it's all about personal preference and tolerance for the level of effort. What I've found out, and wish to share with you here below, is it isn't just about what is the best paint or finish to use, but what is the best combination to use. Some finishes don't play well with paints and colors. Maybe I am giving more than you need, but here's my experiences in a nutshell:
Wood Hardener/sealer - this is a must as a base coat before painting and finishing for woods and cork
Nail Polish: a good but not perfect paint choice, especially for detail work and small bodies. Larger bodies take time to cover and require several coats. It expands under heat - Will bubble up under summer sun if applied to body that hasn't been sealed, even if overcoated with clear Hard-As-Nails. Epoxy top coats, however, will help prevent bubbling.
Latex Paint: if it is water-based, then OK to work with, but oil-based is a paint to clean up with small brushes. Oil based will also yellow under influence of sunlight.
Enamels: hobby model paints fit this category and are a good choice for detail work and covering small bodies. A little more effort required for clean-up
Acrylics: one of the better choices to work with - can either be opaque or transparent. If you are into air-brushing, you can't beat the control and color blending. Aerosol acrylics are good for applying solid colors, but shouldn't be considered on the same plane as air brushing.
Permanent Markers: The Copic system and Sharpies are ubiquitous here. ProMarkers are the best for color saturation and longevity under the elements. Time consuming to color a whole body with a marker. Marker colors are transparent. NOTE: permanent marker colors will bleed through acrylics and latex paint applied on top of the marker colors.
Clear Nail Polish: Many use it because it is easy to apply and dries seemingly hard. But it has a few drawbacks: it bubbles up with little air pimples under heat - the heat of a summer sun. And it also tends to bleed colors color beneath it, except for acrylics and water-based latex. Don't apply over some enamels and all permanent markers. Test before use.
Clear Acrylics: a good quick choice; apply in several thin layers and should be sprayed not brushed. Clear aerosol acrylic spray cans are comparatively expensive though - $10 or so for one can. Caution that clear acrylics are waterproof for only so long. You notice degradation of the finish of a bug fished for a season. But by the time the degradation occurs, you'll have worn out the bug with fish teeth anyhow.
Water-Based Urethane: Ceramcoat and Loon products come to mind here. Not a very durable finish. It will come peel from the bug body after just a fish or two.
Softex and PlastiDip: I use these for certain frog bugs I make because I like the way it dries with a rubber-like matte finish, much like a frog's skin. But it isn't a very economical coating and is smelly to work with. These products will also make permanent marker colors run underneath, so avoid using with marker-painted bug bodies.
Vinyl Lure Finish: similar to Softex and PlastiDip, but chemically different. Not so durable in my opinion, and more expensive.
UV Cure Resin: a quick replacement for epoxy. Most will cure with a slight tackiness, which I don't like. Plus, it's expensive to cover a bug body with the stuff, since the stuff itself is comparatively expensive to epoxies.
Dipped Finishes: Envirotex Lite and DiamondFinish Clear Coat are EXCELLENT finishes but require extra precaution and a well-ventilated space to work with - noxious fumes. Best for production bug makers, not for onesy-twosy makers like most of us.
5-, 10-, 15-, 30-minute Epoxy: good for quick bugs, but the faster the epoxy cure, the more yellowing and cracking will occur, even within a few weeks to a month or two - sunlight accelerates this. If you have the time, use 60-minute or longer epoxy for bug topcoats. Anything under 20-minute epoxy will quickly deteriorate under the elements - just avoid it. A rotary drying wheel is a must.
Rod Building Epoxy: a really good choice for bug top coats. It's flexible no matter the temperature and will not yellow. Again, a drying wheel is a must.
Flex Coat's Lure Gel Epoxy: this is my go-to bug top coat. Very similar characteristics as rod building epoxy - takes 12 hours to cure to a handling state and 24 hours to cure to full hardness.
So, what do I use? I seal all natural materials with wood hardener first, then use white acrylic as a base coat, as it makes all colors applied on top, "pop". Then I use hand-painted or airbrushed acrylics for decorative painting schemes (or Copic airbrush colors, depending on the color effect I am looking for). I add acrylic or nail polish colors on top of that for spots, dots and detail. Then I coat with FlexCoat's Lure Gel Epoxy.
Disclaimer: I am not compensated in any way for the mention of any products above. And as always, if there are 5 different ways to do something, you'll get 10 different opinions. This is just my experience.