I've had a variety of experiences as both bottom and top - these are my observations!
Doggy-style, bottom on all fours, top kneeling, can be good for inexperienced tops, since your anus is exposed and they're able to see what they're doing / guide their penis in.
I've bottomed for several guys who wanted me flat on my front - this is obviously good for the top, in that there's more friction on their penis from buttocks as well as anus, but it also means the top is in total control - good if that's your kind of thing. I've had some experiences of being fucked 'roughly' in this position, with the top holding me down, which is nice if you enjoy some occasional rough sex.
I've topped some inexperienced guys, and found that side to side / spooning is good, since the bottom has control over how deep you go - there's something quite tender about this position. Similarly, if the top is on his back, and the bottom squats down and rides, that gives them control over speed, etc. Also, this position means the top can masturbate the bottom at the same time.
I personally really enjoy being on my back, with my knees raised to my chest / face-to-face - it's obviously erotic to see your lover's face and be able to kiss, and this position means the top can thrust deeply.
As a top, I also enjoy standing, with the bottom bending over and supporting himself on a piece of furniture - good since no-one has to support himself on arms alone..