A 69 position is also comfortable for mutual cock sucking. I prefer to be on top as I find it allows me to better swallow my man's cock and I find the bobbing up and down on a cock is easier on my neck than laying on my back and having him drive his cock down my throat, personal preference.
If your lover has a normal (4-6 inch) length cock then the most erotic position is to kneel before him on a pillow and let him fuck your face. My current lover and I kneel before a wall of mirrors where we can both glance sideways and see what is going on. He loves me to start the sucking but as he gets into the mood he grabs my head and fucks my face until he ejaculates.
Speaking of ejaculation you have various options; swallow or let your lover ejaculate down your throat. Pulling out and leaving only the cock head in your mouth lets you enjoy the force of his ejaculation and the taste of his semen. You then have the option of laying or sitting back and enjoying the ejaculate in your mouth before you swallow or even share some of it back with your lover. I love the taste and texture of semen and take my time savoring it as long as I can before I noisily swallow, something my lover likes to see and hear.
Some men like to continue the power trip after face fucking by cumming on you, it's a dominance thing and I for one am completely comfortable having him cum all over my face. If he cums a lot I often get a mouthful before he pulls out and sprays all over my face. He will often use his erect penis to gather up his semen from my face and feed it to me, something we both enjoy. I was at a local bathhouse once and I had 4 men cum on my face and I walked around the bathhouse naked with their semen dripping from my face, my own badge of courage. Finally one man was so turned on by my semen soaked face that he sucked me to my own orgasm and swallowed my cum.
If you wish to extend your lover's erotic enjoyment there are several ways to help him stop cumming prematurely. As he gets close, you can tell by the flaring of the cock head you can pull him out of your mouth and tightly encircle his cock at the base with your thumb and forefinger. This dampens the feeling and further delays orgasm. Another manner to stretch out his orgasm is to place a small ice cube in your mouth as you begin to suck his cock. The cold temperature temporarily deadens the nerve endings that are primarily in the cock head and delays orgasm until everything melts and warms up.
If you wish to extend your lover's erection (without the use of that little blue pill) take a wide elastic and place it over his cock and balls. This keeps the blood in the penis and keeps it stiff longer. Whether it will stay stiff after he ejaculates is another matter. Most men require some recharge time before they can cum again, they may be able to get an erection quickly after orgasm but cumming again is another matter. I allow my lover 10 or 15 minutes after he ejaculates into my mouth before I attempt to bring him off a second time. Often I will play the subservient sex slut by my voice and ask him if he would like to fuck my ass and that helps his erection to return and him to have another orgasm as he uses my ass to get his rocks off.