If you have a moderately dense soil and beds of moderate width, I would suggest the following:

• If you want to loosen deeply—say, 14 to 16 inches—I would go with a four tine broadfork of corresponding tine length.
• If you are going to loosen shallowly—say, 10 to 14 inches—you might choose a tool with fine tines.
• If you loosen only six to 10 inches, you could use a wider tool with more tines—say, a 30-inch wide fork with 8 tines of appropriate length.

Generally speaking, the wider the tool, the shorter the tines. The deeper you go, the fewer the tines.

When using a broadfork, technique is everything. Dig a foot wide trench across the end of the bed and work backward in two to four-inch spits, driving the tines straight into the earth then pulling back to loosen the spit and pushing forward to deposit it on the far side of the trench, then dragging the fork back another two to four inches, repeat the same process. If you have highly amended sandy loam you can take a four to six-inch spit.

When making your decision, consider—in addition to your soil type and bed width:

• Soil moisture and compaction.
• Season and day lengths (There’s no need to till way deeper than any plant roots will penetrate in a season.)
• Personal size and strength. A four tine broadfork with 16 inch tines weighs in at 25 pounds. A 30-inch wide tool with 12 inch tines can weigh upwards of 40 pounds.
• Presence and size of field rocks and/or roots of trees and shrubs.

It is better to start with a manageable tool and move to a bigger one as your skill develops than it is to start with a behemoth that discourages.