The only benefit a mechanical mod has over a regulated mod is it won't stop working due to an electronic breakdown - a good quality mech should last a lifetime with regular maintenance. An electronic device is more convenient and will provide your chosen output throughout the life of the battery with the added convenience of being easy to change output, up or down, at will - a mech can't do this and will only provide what power is available from the battery to your coil, and the vape intensity decreases as the power in your battery does.
I'm currently only using mechs, I like the clean power delivery of a mech, something I notice and appreciate over an electronic device.
I'd definitely recommend a 21700 mech purely as the 21700 batteries are a big step up from 18650s - the highest amp rated 18650 is the Samsung 20s at 30a but it only has 2000mAh (mAh is essentially battery capacity/how long they last for) the Samsung 30t is a 21700 battery, is capable of 35a and has 3000mAh, so you can run a lower resistance with a third more runtime. But it really depends on the resistance you plan to run - the two cells I've listed above are the best on the market for low resistance in their respective sizes, the 18650 Samsung 20s can be run at 0.14, the 21700 Samsung 30t at 0.12,but you'll get far greater run time on the latter.
Building a bit higher at 0.17 allows the use of the excellent 25a cells in both sizes, the Sony VTC5a or the new Molicel P26A are 25a/2600mAh in 18650 size; the Samsung 40t is 21700 sized and 25a rated, but they have a massive 4000mAh capacity! That's a lot of extra runtime!
You definitely change your batteries out more frequently on a mech due to the vape output between a fully charged and even a half charged battery having quite a difference in said output (resistance dependant of course, the lower the resistance the more noticeable battery drop off is) - I've no way of measuring but I change mine at roughly half charge from full.
Can't really recommend a 21700 mech as I've yet to use one, and the only 21700 I have my eye on is the Kennedy Vindicator which is hard to justify to anyone at £130! I'd probably avoid the Bonza as some apes have reported poor performance from it due to the poor switch (the atty is excellent though!) The Tauren by THC is well liked by mech users on here and is available for £35 from SR Vapes.
