Lately I've been revisiting MySQL frontend tools in context of web hosting and HeidiSQL clicked with me almost immediately as light yet feature-rich client.
What it does
As any tool of such kind the task HeidiSQL performs is quite defined - connect to database(s) and retrieve or manipulate data. So difference between tools boils down to performance, convenience and extra functions that go beyond running simple SELECTs all day long.
This one scores nicely on all:
database is accessed directly;
interface is very responsive and sufficiently visual;
there are plenty of functions to make life easier.
As for general usage I like that app has live log that displays any and all operations you perform - both those run explicitly by queries and anything else like just navigating around. It is good reference, educational and queries from there can be quickly copied as text or into new query tab via context menu.
Among more impressive functions - export implementation is great. While going through exporting/importing through a file is no-brainer in most tools, HeidiSQL actually allows you to set up transfers between different servers. Not much difference on technical level, but huge improvement to the workflow.
Oh, and global (as in whole database or server) search. I wish someone told me about this some years back.
While export/migrate is very impressive, import is somewhat more basic - SQL and CSV. Good enough, but stuffing some Excel file into table would seem common enough task to be supported.
At times interface gets confusing (in how-do-I-unpress-what-I-just-pressed fashion) and also a little glitchy (like buttons on toolbar duplicating).
Snappy and functional open source app with native portable version available. Doesn't quite compete at level of commercial front-end monsters of a software, but still very useful.