Both Fujimura-kun Mates and D-Frag! are gag manga about a delinquent guy hanging out with a handful of out of ordinary girls. The style of humor, characters lacking common sense and hilarious punchlines make those two series a good match.
The main selling point, aside from a delinquent surrounded by oddball characters, is the humor. Straight man/funny man, punchlines with proper timing, a bit of wordplay and truly, seriously, the punchlines. The main delinquents for both series are masters of the art!
Both these manga revolve around a delinquent male who somehow gets dragged into a group of insane girls who seem to do nothing but make his life more difficult.
The comedy is of a high standard in each, with excellent punchlines everywhere, fun characters who say random things at the funniest of times, some great wordplay and even a few quality references thrown in for good measure.
Fans of one should find the other an enjoyable read.
Fulimura-kun Mates and Choku have one thing in common, both of those manga feature a perverted girl with (quite) a few loose screws. In both cases it's really hilarious (though Eri is more awesome). If you liked one of those manga, you have to check the other one as well.
In both manga the male lead who is believed to be a delinquent by everyone, finds himself an unwanted harem of totally messed up girls (which he would rather not have). Those girls are different between those two series, but if you found one of those manga funny, you could try reading the other one too.
Both of these mangas have similar characters and similar story styles. In both Delinquent styled males leads meet some rather odd girls.
In fact they are nearly twins in the sense of the character styles and story set up.
However I believe Bokutomo to be the better of the two, as the characters are stronger and the story is more down to earth. Im sure if you liked one you'll at least be amused by the other..