Below are some of our suggestions on what to look at for a good set of ratchet wrenches for a DIY Mechanic.
GearWrench 20-Piece Ratcheting Wrench Set, SAE and Metric http://amzn.to/2jVmAbK
DeWalt DWMT72169 Reversible Ratcheting Wrench Set (10 Piece) http://amzn.to/2kVGWC1
TEKTON WRN53190 Ratcheting Combination Wrench Set http://amzn.to/2jXDYPB

What Type of Ratchet Wrench? - Ratchet wrenches are available in a variety of styles for a variety of applications. Like all the other tools in your tool box, they fit a specific need and in many ways solve problems. Ratchet wrenches are used in similar ways to a socket and ratchet, but in many ways a ratchet wrench can be much more useful. They fit into smaller areas and allow a much better line of sight to what is happening around the fastener.
Ratchet wrenches are made in many different styles and they all seem to have a place, in fact many mechanics will have multiple types of ratchet wrenches. so if you are in the market, don't look for the cheapest set on the market, look at the features. when we were shopping we thought the swivel head types would be a bit awkward to use but we were proven completely wrong and now mostly use swivel head models.

While the price of the models will differ, most of the cheaper models will be a straight ratchet wrench. There are fewer moving parts and they cost less to make. The next highest price will be the swivel head and further on up the reversible ratchet wrench. note there are tiers of quality and warranty in each type so pricing will overlap.

Ratchet Wrench Uses

Tightens / loosens nuts and bolts.
Metric and standard sizes.
Ratchet action on one end moves freely in one direction and engages the fastener in the other direction to tighten or loosen without removing the tool.
Some have pivoting ratchet ends for use in tight spaces.
Where to Start?

If you have never purchased or do not have ratchet wrenches in your tool box, look for a specific area that you would need these wrenches. In many cases, people might not have stubby wrenches or they might not have a swivel type wrench to get into tight areas. Try to fill that niche with this purpose.

Most will start out with the simple standard or metric set of swivel heads as they are moderately priced and wok in many situations. Stubby ratchet wrenches are also popular as a first purchase because they are made for small and tight areas. We normally would not recommend that someones first purchase of a ratchet wrench set be reversible because of the extra cost. The reversible ratchet wrenches absolutely rock, but the cost is normally double of the standard or swivel head. That means you get half the tools for the amount spent.