"What sort of oven should I buy?"
"What's the better option - an OTG, a microwave oven or a conventional oven"
So here are the different options you need to consider. All of them differ in cooking method, price, etc. Consider the space you have in your kitchen, your budget and what sort of use you have for your oven before zeroing in on one.
(a) Conventional ovens
Conventional ovens work on an electric element for cooking or a gas burner. In this type of oven, heat radiates up and pushes cold air down which can lead to uneven cooking or baking. However, this type of oven is very common and usually inbuilt in kitchens or come as part of the kitchen range.
(b) Convection ovens
Convection ovens cook food a bit differently. There's a fan at the back that forces air circulation throughout the oven, cooking food more evenly. This also results in quicker heating and is said to consume less power. The cooking time will differ from that of a conventional oven.
(c) Microwave Ovens
These are the 'ovens' that most of you probably own. They are most popularly used for heating and defrosting and use radio waves for this. There are some microwave-oven-specific recipes that are best for baking in a microwave. If you try a normal recipe in the microwave, it may not work out well so don't make that mistake.
(d) Microwave cum Convection Ovens
These are the rage now! Its a microwave oven that has a convection oven option, which means, when you turn a knob, your microwave turns into a normal oven (convection type) and you can bake your cakes and cookies and anything else, as usual following the usual recipes. Some of these ovens also come with a grilling option and you make use of that feature too. There's a very useful FAQ on DK's blog and you can read more about this here.
(e) Oven Toaster Grill (OTG) Oven
These use old-fashioned filament coils for heating and cooking (much like a geyser). Although they work fantastic for making toast and even grilling, baking in them doesn't work out as best as in the other ovens. Before I moved to Singapore, I had an OTG in which I used to bake and although the food turned out just fine, sometimes, the crust used to dry out or the cake used to get unevenly cooked. I made these Triple Chocolate Fudge Brownies and my first No-Knead Bread in an OTG and although they tasted just fine, I am sure they would have come out much better in a convection oven.
I have a post coming up from Aparna who has a MW Convection oven, who will talk about her experiences.
This post and information on it is based on my research. I claim to be no expert so if you find anything wrong or unclear, do drop a note.