Straight drive is relatively easy and the batsman doesn’t have to use a lot of skill.
First, the ball is almost always pitched at full length, and in the line of stumps, so it makes the batsman’s job a lot easier (You don't always attempt to play a good solid straight drive on the up on ball at fourth stump).
Second. There is less risk involved. Since the bat’s face is fully behind a full pitched ball, chances of an edge are low. We rarely see a batsman driving straight but getting caught behind.
Third, you only have to beat one fielder, and that too, at a very close proximity - the bowler. Once you pass him with a solid hit, there is no stopping the ball.
Playing a drive in the covers area requires a little more skill and dares a little more risk.
First, you have to pierce a gap between 3 fielders who are quite far away, and always ready, alert and expect the ball to come their way. They have plenty of time to dive n save the boundary, unlike a bowler in his follow thru.
Second, Since the bat comes at an angle and meets the ball in half way (say ball is travelling in a straight line towards the wicket keeper at 4th stump, and the bat comes down from leg stump towards covers to meet the ball near the creeze) there is an element of greater risk of a snick - we have seen it quite often.
Third, cover drive on the up, opens up a great possibility of a catch. We have seen some caught n bowled by the bowlers on batsmen attempting to play a straight drive but risk is less for the batsman. It doesn’t happen as much and it’s very hard for the bowler to hold onto a solid hit at close proximity - so usually the odds go in the favor of the batsman.
For me personally, COVER DRIVE ALL THE WAY, especially when Baber Azam is batting in a Test match. And his straight drives are also a delight to watch.