which is a better speaker

I liked the Pioneer HPM100’s when I first heard them. JBL has always been a favorite and slightly more efficient. Between those two I would choose the JBL’s.

Not a fan of either. Pioneers had a nice tweeter, but that's about it. JBLs were built better, but boomy and hardh. Find a pair of JBL L-110s ca. 1980. Those are killer, will be very happy driven by a 2265B. JBL got all the pieces right - it was the first ported speaker I ever heard with extended, tight bass. The soft dome tweeter was a vast improvement, and everything could keep up with the LE-5a midrange. Add to that mid and tweet level controls and impeccable build quality and you have a classic.   

As for the 2265, Marantz always had ballsier receivers because they had better power supplies and discrete transistor high current output stages. This was why they also tended to cost a bit more than the Pioneers and Kenwood's of the day.

I worked in a shop that sold tons of Advents, a speaker known to blow tweeters when pushed. The high watts/dollar receivers were heavily current limited to protect their wimpy output stages that only performed well into an 8 Ohms resistor. Rather than damage the output stage, current limiting essentially clipped the amp at a level low enough to not hurt the outputs and dumped the resulting trash into the speakers. This was marketed as a feature that protected the amp. We rarely saw blown speakers driven by Marantz and HK, blown tweeters were common with Pioneer and Kenwood receivers. 

I agree they both kind of stink. Have very little experience with the Pioneers, but all older JBLs I have heard are pretty bad sounding.

I am not familiar with the equipment but based on comments above that it is designed for rowdy reproduction of rock I would recommend Zu Audio.  You don't mention what your budget is but they have extremely reasonable offerings for every budget.  You can also find them used online at times.  I do not own a pair but have read many, many positive reviews.  They offer 60 day in home trial which addresses some of the recommendations of others.

@mike317 

To be fair, as posed your question is difficult to answer meaningfully.  What kind of music do you like to listen to, at what volumes and in what size of a room? Are you listening in one position or moving around?  Can you describe what kind of sound you like?  Without more information, the best anyone could do is look at the specifications for the equipment in question to see if there are any glaring mismatches, especially with regards to impedance and power.  There are lots of charts online showing frequency response, impedance (I didn't see any in a quick search but I'm sure they exist), off axis response, etc.  

Both speakers are 8 ohms, a good load for this receiver.  I don't have their respective impedance curves to spot any weirdness, but I would think it unlikely for mass market bookshelf speakers to have crazy impedance dips that could stress a power supply.  

The Pioneers are 92.5dB efficient with 50W power handling; the JBL are 89dB with 250W power handling.  So they are fairly close in output.  The Marantz will be able to get more volume from the HPM-100s because it doesn't have the juice to push the JBL to their limits.  

I have heard the Marantz 2265b and many of its brethren.  I grew up with a 2252B but many years later found I preferred the 2270 for it's more euphonic sound.

I have heard neither speaker, so can't comment on their respective sound signatures and how those might or might not jibe with the Marantz.  But they are both very well known.  The Pioneer was designed by Bart Locanthi, I believe, and was very well received.  The JBL is from a line with a tremendous pedigree, culminating in the 250ti, which I think is an "audiophile" speaker by today's standards.

I will however, echo something a previous poster noted, which is that if your receiver is all original, it will definitely not be sounding up its potential.  Electronic components age and, if you love this receiver, investing in an overhaul will keep it running nicely for decades to come.