Hi,
I would suggest these steps.
1) fix your min and max budget.
Go to flipkart and search for models that fit your range. It has the best selection and compare tool.
2) Special attention should be given to the Type of Display, Display resolution, Onboard ram and particularly the Processor and its performance benchmark.
For i3 alone comes in many flavors, speeds and performance. The price of i3 (or for that matter i5 or i7) differs hugely according to its performance.
To check the performance you may use
https://www.cpubenchmark.net/cpu_list.php
It has listed practically all the processors of both Intel and AMD and their variants. This should give you a fairly good idea about what you are paying for and what you are getting.
Addition graphics card and memory will cost more and so decide whether you want it or not.
In my opinion it is best to have these. The performance increases dramatically. The difference shall be in unloading / loading softwares, etc. The reason is that widows displays are images and the time taken for screen refresh changes with graphics card and memory.
Look for accessories that comes with the laptop. carry bag, headphones, battery charger etc etc.
Look for warranty, accident warranty, additional warranty etc etc.
Finally hunt for the best price for the modal you want
Offline , try reliance world, bigbazar etc. They sometimes announce special discount offers too.
Do not go for sony, toshiba etc. They have practically stopped this stream of business.
Lenovo has two ranges : lenovo range as well as thinkpad range : Thinkpad range are IBM modals originally.
Cheap modals of International brands comes with cheap parts, mostly specially made for India (these modals may not be available in say USA etc or the specs will be different).
For trading and most of the work, a 15inch screen is best.
Look for the keyboard. Most of the newer lappys do not provide additional port to connect your tv. So if you want to connect your TV directly to your lappy, buy one that provides the display port.
a few months back , I wanted to buy one and finally settled for HP 15-p27tx. I got it from big bazar at very good price.
Hope this helps you