(2D graphics/style question very linked to gameplay design so I put it here)

Im switching my rts from medieval to modern style, but still have two very different ideas/design decision to choose from:

On the left: traditional RTS seen from above, rotating turrets and vehicles. Problem to make graphics for buildings and more work with units as well

On the right: abstracted icons for units and buildings. No rotation, units simply slide like in many turnbased war games.

Terrain is also harder to do in the left version, so likely i will go for a desert setting with little to no vegetation. The right version would have more abstracted terrain types such as "forest" and "hills", more like a map than actual terrain.

What is your input? Left version will probably be easier to make more action oriented, while right can be more tactical with different terrains and easier to add stuff like "fortify position" (just add icons for that since no need to animate).

However, right version feels much more stiff and lifeless as nothing can rotate...

(best would probably be to do all units in 3D and render 8 direction of it from an angled view, but no resources to do that)

Since the scale on the right would be bigger, you can even have different biomes that change the terrain significantly.

I would totally prefer the right one if the game is turn based.

You have much more possibilities with this version and not nearly as much problems with transformation code.

Usually you want to have rotation in turn based games only if the rotation is meaningful.

For example if you have a tank that is less armored in the back or can only fire in the front, you have to make sure it's facing the right direction.

If the rotation does not matter, why bother with the code?

Pick a style that makes less effort when creating and using so you can put more resources into creating content (more difference in units, more maps, story, etc.).

Gameplay > Content > Visuals

If a game looks nice but plays strange or even bad, you won't have many player going through a lot of the game.

If a game looks strange or bad but plays really well, you might even get a big community (think Minecraft or other abstract games).

Are those assets your own creation?

If yes, keep the right for sure, that style looks really good on turn based games.

The assets on the left would make a good RTS if you ever want to make one.

Take a look at the Battle Isle Series which might be nice for reference.

Left side looks more arcade and casual, right side looks more tactical and realistic.

I prefer right side, that'd be really cool in real time. The reason is that with this level of abstraction, you can have much more realistic and deeper tactics. In real life, their would be thousands of foot soldiers for a couple of tanks. With the left side, you'll usually have 1 tank for 5 infantry. The visuals are more realistic, but the game is a lot less convincing because you know that individual soldiers don't fight like that. On the right side, you can abstract 10 tanks in 1 tank unit and 1000 soldiers in 1 infantry unit. The abstraction makes it look a lot more convincing because you use your imagination to picture the actual soldiers doing the fighting.

If you want to simulate directions and rotations of units, you don't need to have rotatable sprites, just draw a cone which shows which direction this unit is facing and its attack range at the same time.

I do like arcade games, sometime i play turn based too. 
By your explanation, i think the difference between left side and right is the playing style.

For the left side, what can be offer to the player are much more actions, such : player skill to aim shoot, evade foes bullets, utilize building trees to snipe from afar, sneaking (if AI implement sight range of awareness). Or maybe how fast player can disable foe's unit factory, before it swarm legions to push the player, should i take down all foes first, or direct ride to the base.
Also can use bullet styles short spread or hard long range, area effects, etc.

For the right side, do you mean to create team or single character control? 
If turn based style, i prefer team play, mean i can have mix of characters with various abilities and weapons of each, bullets stock or unique devices to carry. Player will be busy for their vehicle positioning at terrains, plan a combo/sequence attacks, or prepare team weapon setup for the next couple of turns.