I have hundreds of hours in my current game.
The overturned Orinocco is my "Favourite" ship.
I spend more time in that beast than all my other ships combined.
Until 1.4 I would have said my favourite M3 was the Bayamon but the Khaak M3 is too accurate these days to go for only 10MW of shields
The Orinoco is by far the most versatile M3.
The Nova is a tank - it gets you there but it's such a beast to get anywhere.
The Falcon is just bad. Too slow to do anything other than carry fuel for my M2.
The Mamba is for speed junkies - underweight but BOY can it move!
I haven't spent much time in the Perseus - the small cargo bay completely kills it for me.
I know next-to-nothing about the Baracuda. Despite all the time I've spent in the X universe I just can't bring myself to spend much time in a Boron ship.
The Xenon L isn't worth talking about in a serious discussion about M3s.
The Khaak Fighter isn't worth talking about - it's so seriously overpowered it doesn't bear thinking about. The only time I've seen it struggle is taking down an Osprey or any M2/M1. The rate of damage isn't high enough to deal with 375+ MW.
Finally the Iguana - This does belong in the list of heavy fighters. Even though it turns like a bus it hits so hard it's ridiculous. Until Capturing with IDs was nerfed this was my ship of choice. Now I fly something that can mount PSGs for capturing.
And if we're going to branch out into TPs, what about the TS combat king - the Demeter! Armed with a PSG and a Mining Laser this thing will hold its own against a large cluster OOS and do a good job in sector too.
I had a wonderful time using one of these going mobile mining. Out in the badlands where the pirates roam free I took many scalps and captured many ships in that beastie. It's a shame its so slow ...